HOSTOMEL, Ukraine—Russian forces moved by air and land to attack Kyiv on Friday, hitting defenses across Ukraine that U.S. and British defense officials said were unexpectedly strong, while Moscow signaled openness to holding talks with the Ukrainian government.

Despite the overture, Russian President Vladimir Putin Friday verbally attacked Ukrainian President Volodymyr Zelensky and his government, comparing them to terrorists.

“They...

HOSTOMEL, Ukraine—Russian forces moved by air and land to attack Kyiv on Friday, hitting defenses across Ukraine that U.S. and British defense officials said were unexpectedly strong, while Moscow signaled openness to holding talks with the Ukrainian government.

Read live updates on Russia’s invasion of Ukraine

Despite the overture, Russian President Vladimir Putin Friday verbally attacked Ukrainian President Volodymyr Zelensky and his government, comparing them to terrorists.

“They hide behind people in the hope of later blaming Russia for the civilian casualties,” Mr. Putin told a security council meeting. He said Russian forces in Ukraine weren’t fighting primarily with regular Ukrainian army units, but with “nationalist formations” that he said without presenting evidence were conducting genocide in the country’s east.

After dark on Friday, Mr. Zelensky released a selfie video of himself standing in front of the presidential headquarters in central Kyiv with his chief of staff, the country’s prime minister, and the parliament majority leader—all of them clad in fatigues. “We are all here, defending our independence and our state. And that’s how it will be,” he said, as Russian media spread rumors of him having fled the city.

Mr. Zelensky also spoke by phone with President Biden late Friday. A White House official said the call lasted about 40 minutes. Mr. Zelensky wrote on Twitter: “Strengthening sanctions, concrete defense assistance and an anti-war coalition have just been discussed with @POTUS.”

The Biden administration is considering additional support to the Ukrainian military, but defense officials have declined to speculate publicly about what form that might take or when any additional assistance might be delivered.

Kremlin spokesman Dmitry Peskov earlier told reporters that Moscow was willing to send a delegation to the Belarusian capital, Minsk, according to Russian news agencies, saying that representatives would include officials from the defense and foreign ministries as well as the president’s office. The offer followed a video statement by Mr. Zelensky calling on Mr. Putin to meet for talks.

Russian Foreign Ministry spokeswoman Maria Zakharova followed up Mr. Peskov’s offer by saying that Russia was ready for negotiations, but the goals of its military operation remained.

Moscow’s offer came on the second day of fierce combat across Ukraine, as Russian forces pouring in from neighboring Belarus through the Chernobyl nuclear disaster exclusion zone reached the outskirts of Kyiv. They took over the Hostomel airfield following an airborne assault on Thursday, and by Friday morning Russian armored forces reached the area. Heavy combat continued through the day, and Ukrainian troops blew up several bridges leading into Kyiv from the northwest.

Explosions and gunfire rocked Kyiv as Russian troops intensified attacks on Ukraine’s capital. Residential areas were hit and people sought refuge, while Ukrainian President Volodymyr Zelensky called for help from Western leaders. Photo: Umit Bektas/Reuters The Wall Street Journal Interactive Edition

Russian forces made some progress Friday but remain behind what analysts expected them to have captured at this stage of the attack, security officials said. Ukrainian air power and air defenses remain partially intact.

U.S. officials had assessed as recently as Thursday that Kyiv could fall within 24-48 hours. U.S. officials still expect it could fall, but a senior defense official said the Ukrainians had slowed the Russians’ push into the capital.

The official said an amphibious assault was under way west of Mariupol, a large city on the Sea of Azov.

Ukraine’s strong resistance raises fears among Western officials that Russia might use more indiscriminate artillery fire to accelerate its attack. So far Ukrainian forces have ceded rural territories to focus on defending urban areas. The officials say Russia’s primary aim remains to encircle Kyiv and force regime change. Meanwhile, forces heading south from the Ukrainian city of Kharkiv aim to encircle battle-hardened Ukrainian troops in the east of the country. Some 10,000 members of the Chechnya National Guard may be heading to Ukraine potentially for occupational duty, they said.

The stiff Ukrainian resistance was evident Friday as troops—including recently enrolled volunteers in civilian dress—took positions in hastily dug out trenches in the woods around Kyiv. With Ukrainian artillery and armor dispersed nearby, they braced for a Russian offensive. The Ukrainian capital faced a second day of bombardment on Friday and Mr. Zelensky vowed not to surrender.

Ukrainian President Volodymyr Zelensky, addressing the nation in Kyiv on Friday, told EU leaders, ‘This might be the last time you see me alive.’

Photo: UKRAINE PRESIDENCY/AFP/Getty Images

Mr. Zelensky late Thursday told a gathering of European leaders by video, “This might be the last time you see me alive,” according to two European officials familiar with his comments. “I don’t know how much we’ll be able to hold. Russia is shelling civilian targets.”

A senior EU official described Mr. Zelensky’s call as harrowing and “chilling to the bone.”

EU officials at the same meeting agreed to impose sanctions on Mr. Putin and Russian Foreign Minister Sergei Lavrov, according to three EU officials and diplomats.

By early afternoon Friday, reinforcement columns of Ukrainian armored vehicles drove into Kyiv as fleeing city residents, whose vehicles clogged the outbound lane, got out of their vehicles to cheer and flash victory signs. Ukrainian Mig-29 jet fighters roared low overhead, showing Ukrainian insignia on their wings—a sign that Russia, despite its formidable advantage in aviation and two days of relentlessly bombing Ukraine’s air bases, still hadn’t achieved full control of the skies.

In the late morning, gunfire erupted in several Kyiv neighborhoods, in what Ukrainian officials said were clashes with Russian infiltrators, some of them dressed in Ukrainian uniforms. Municipal crews erected obstacles with concrete blocks and heavy trucks around the city center. Ukrainian artillery and tanks were moving through the city, and thousands of volunteers lined up at recruitment centers to receive weapons. On the roads south of Kyiv, armed villagers made their own roadblocks out of tractors and sandbags.

Russian soldiers and armored vehicles moved Friday towards mainland Ukraine on the road near Armiansk, Crimea.

Photo: epa/Shutterstock

Casualty figures were unclear, but each side put the other’s death toll in the hundreds. Ukraine said dozens of civilians also died in Russian airstrikes on its cities.

The Russian Defense Ministry said Russian troops had captured the regional city of Chernihiv, north of Kyiv, a claim Ukrainian officials denied. Battles were raging around eastern Ukraine’s main city of Kharkiv, just a short distance from the Russian border, and east of the southern city of Kherson, attacked by Russian forces that pushed from Crimea.

In Kyiv, Russian airstrikes shook the city center before dawn, and continued sporadically through the day. Thousands of residents of Kyiv spent the night in underground subway stations that had been converted to bomb shelters. A residential high-rise went up in flames after being hit in the east of the city.

“We are defending our country all alone,” Mr. Zelensky said Friday, wearing a military sweatshirt. “The most powerful nations of the world are just watching from afar. Only solidarity and decisiveness by Ukrainians will be able to preserve our freedom and our state.”

Mr. Zelensky said he is Russia’s principal target as Moscow seeks to bring down Ukraine’s democratically elected government. “The enemy has marked me as enemy number one,” he said. “They want to destroy Ukraine politically by destroying the head of the state.”

Russia’s continued bombardment of Ukraine has forced many to make the difficult choice between fleeing the country or staying put. WSJ’s Brett Forrest in Kyiv, which was increasingly targeted, explains how people are weighing their options. Photo: Vadim Ghirda/AP The Wall Street Journal Interactive Edition

Mr. Peskov, the Kremlin spokesman, said Friday that Moscow recognizes Mr. Zelensky as Ukraine’s president.

The bombing in Kyiv on Friday was much heavier than Thursday’s airstrikes, which also hit residential areas. Just past 4 a.m. in Kyiv’s Darnitsa neighborhood on the east bank of the Dnipro river, large fragments of a ballistic missile struck a complex of residential buildings, according to military officials at the site. Rescue workers said there were fatalities.

Reports, which were conflicting, suggested the blast resulted from a drone or a missile downed by Ukrainian air-defense forces. One man said he was at home when the strike happened. “I went out on the balcony to have a smoke and something hit,” he said. “Now I can’t hear anything.”

The explosion carved a crater in the ground at the base of a 10-floor apartment block and blasted completely through scores of apartments, blowing out windows on either side. Fires lighted up the night sky. The windows of a kindergarten 50 yards from the blast were also blown out.

Dazed residents wandered the site hours afterward. Roman Karmazin, 47, gathered what clothes he could carry, including shoes for his 6-year-old son, Artem. “What are we going to do now?” he said.

Ukrainian soldiers braced to defend Kyiv as their Russian foes approached the capital.

Photo: Emilio Morenatti/Associated Press

Fragments of a downed aircraft in Kyiv.

Photo: Oleksandr Ratushniak/Associated Press

“Last time our capital experienced anything like this was in 1941, when it was attacked by Nazi Germany,” Ukrainian Foreign Minister Dmytro Kuleba said on Twitter. “Ukraine defeated that evil and will defeat this one.”

Ukrainian officials said Russia had attacked on a wide front along the country’s frontiers from Belarus to the north, Russia to the east and Russian-controlled Crimea in the south. They met strong Ukrainian resistance.

Video shows Russian tanks crossing the border, airstrikes hitting several cities and long lines of cars fleeing after Russian President Vladimir Putin announced a military operation in Ukraine. The U.S. and its allies condemned the invasion and announced further action against Russia. Photo: Sergei Grits/Associated Press The Wall Street Journal Interactive Edition

Russia has failed to take any of its main objectives in the first wave of the attack, said U.K. Defense Secretary Ben Wallace. “It is behind its hoped-for timetable,” he said, adding that Russia had lost 450 personnel during the offensive.

By nightfall on Thursday, Russian forces had captured the now-defunct, Soviet-built Chernobyl nuclear power station, the site of the world’s worst atomic energy disaster, and the surrounding exclusion zone, Kyiv said.

People sheltered inside the Kyiv subway on Friday.

Photo: Efrem Lukatsky/Associated Press

Residents of Kyiv waited to board an evacuation train to Lviv on Friday.

Photo: UMIT BEKTAS/REUTERS

The White House said it had credible reports that Russian soldiers were holding staff at the nuclear site as hostages. Videos posted by Ukrainian authorities showed evidence of fierce fighting around the country, with downed aircraft as well as damaged tanks and armored personnel vehicles from both sides.

President Biden called Mr. Putin’s move an unprovoked, unjustified attack and said the U.S. would impose new sanctions on Russian banks, the country’s elites and its largest state-owned enterprises, ramping up Washington’s efforts to punish Moscow.

“Putin is the aggressor. Putin chose this war, and now he and his country will bear the consequences,” Mr. Biden said during a speech at the White House on Thursday afternoon.

The offensive—for which around 190,000 troops were massed around Ukraine—amounted to Mr. Putin’s most aggressive move to redress what he views as Russian losses since the collapse of the Soviet Union, the end of the Cold War and the expansion of the North Atlantic Treaty Organization and the European Union toward Russia’s borders.

Ukrainian refugees crossed the border from Shehyni in Ukraine to Medyka in Poland on Friday.

Photo: Michael Kappeler/DPA/Zuma Press

—Bojan Pancevski, Laurence Norman, Max Colchester, Andrew Restuccia, Gordon Lubold and Nancy A. Youssef contributed to this article.

Write to Yaroslav Trofimov at yaroslav.trofimov@wsj.com and Brett Forrest at brett.forrest@wsj.com