KYIV, Ukraine—Ukraine’s president warned Saturday of a “new stage of terror” by Russian forces in Ukraine, after what he said was the kidnapping of a mayor in the south of the country as well as a fresh round of airstrikes on the outskirts of the capital.

Cruise missiles slammed into an airport south of Kyiv, setting fire to an oil terminal and an ammunition depot, authorities said. Russian strikes also hit suburbs to the east and west and a drone crashed in the center of the city after being shot down, setting fire to a bank,...

KYIV, Ukraine—Ukraine’s president warned Saturday of a “new stage of terror” by Russian forces in Ukraine, after what he said was the kidnapping of a mayor in the south of the country as well as a fresh round of airstrikes on the outskirts of the capital.

Cruise missiles slammed into an airport south of Kyiv, setting fire to an oil terminal and an ammunition depot, authorities said. Russian strikes also hit suburbs to the east and west and a drone crashed in the center of the city after being shot down, setting fire to a bank, officials said.

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The stepped-up missile strikes and bombings came as Russia repositioned its ground forces for what was expected to be a new push to encircle the capital, Western officials said. For more than two weeks, Ukrainian forces have managed to hold off Russian attempts to push into Kyiv, while attacking Russian supply lines and destroying tanks and other armored vehicles.

Armaments supplied to Ukraine by the U.S. and its European allies—especially antitank and antiaircraft weapons—have played an important role in checking Russian advances. U.S. Vice President Kamala Harris has said new weapons are being delivered daily to help Ukrainians defend themselves.

In a video message, Ukrainian President Volodymyr Zelensky denounced what he said was the kidnapping by Russian forces of the mayor of the southern city of Melitopol. On Saturday, a fresh round of Russian airstrikes hit on the outskirts of Kyiv. Photo: Thomas Peter/Reuters The Wall Street Journal Interactive Edition

On Saturday, President Biden authorized $200 million in new security assistance to Ukraine, bringing the total authorized U.S. security assistance to the nation this year to $1.2 billion, according to a White House official.

Oryx, a blog that verifies destroyed military equipment via open-source imagery and intelligence, said Ukraine has destroyed or captured hundreds of Russian tanks and armored vehicles since the beginning of the conflict, and shot down a dozen planes and 14 helicopters and five drones.

On Saturday, Russia’s deputy foreign minister, Sergei Ryabkov, warned that Moscow would consider arms deliveries to Ukraine as legitimate targets for the Russian armed forces.

“We have warned what kind of consequences the thoughtless transfer of weapons, such as portable air-defense systems and antitank systems, into Ukraine could have,” he said, speaking on state television. “It is the U.S. that is the source of maximum tension.”

Russia has had limited success in disrupting supply convoys or other military road traffic in Ukraine since the beginning of its invasion two weeks ago. Ukrainian troops, tanks and other weaponry on the move are a frequent sight on highways during daylight hours.

Russian President Vladimir Putin on Saturday signaled little interest in negotiations with Kyiv. In a 75-minute phone call Saturday, German Chancellor Olaf Scholz and French President Emmanuel Macron tried to persuade Mr. Putin to agree to an immediate cease-fire and seek a negotiated solution, according to a German readout of the call.

A Kremlin statement said Mr. Putin used the call to describe what he said were numerous violations of human-rights law by Ukrainian soldiers and nationalist groups. Mr. Putin asked Messrs. Macron and Scholtz to pressure Kyiv to stop “criminal activities,” the Kremlin said.

“Have we detected a willingness of Mr. Putin to stop the war? The answer is no,” said a senior aide to Mr. Macron. “The response is that we draw one conclusion…raise the price of the war for him and take new sanctions measures.”

The U.S. and its allies have imposed extensive sanctions on Russia, prompting widespread financial disruption. The Moscow Exchange said Saturday the country’s main stock market would stay closed next week, through March 18. The stock market hasn’t opened since Feb. 25, the day after the invasion.

In a news conference in Kyiv, Ukraine President Volodymyr Zelensky said that Russian forces might be able to seize large parts of the country but that they wouldn’t be able to hold on to any gains. Already, Russian forces have been confronted with protesters in cities they are occupying.

President Volodymyr Zelensky addressed a group of foreign media in Kyiv on Saturday.

Photo: Christopher Occhicone for The Wall Street Journal

In a video address released early Saturday, Mr. Zelensky denounced what he described as the abduction by Russian forces of the mayor of the southern city of Melitopol, who had refused to cooperate with occupying troops and continued to display a Ukrainian flag in his office.

The mayor, Ivan Fedorov, was at work when Russians took him away with a plastic bag over his head, an adviser to Ukraine’s Interior Ministry said.

“They did not find collaborators who wanted to hand over the city and the power to invaders,” Mr. Zelensky said in the video. “Therefore they had to switch to a new stage of terror when they are trying to physically eliminate representatives of the legitimate local authorities.”

While Russia’s ground forces regroup, Russian airstrikes have been pounding Ukrainian cities far from the front lines. Missiles hit airports Friday in the western Ukrainian cities of Ivano-Frankovsk and Lutsk, where attacks have been rare since the beginning of the invasion.

A column of smoke rises from burning fuel tanks that locals said were hit by five rockets at an air base outside Kyiv.

Photo: THOMAS PETER/REUTERS

In eastern Ukraine, three missiles landed in the city of Dnipro, where city officials said an apartment block and a kindergarten were destroyed.

While Russian troops have fought their way to the outskirts of Kyiv in a bid to topple Ukraine’s government, Ukrainian fighters have ambushed convoys along the way with Turkish-made drones and Western antitank munitions.

High casualties among top-echelon officers suggest they are taking unusual risks to prod stalled units forward, Western officials said.

On Friday, Ukrainian officials said the country’s forces killed Russian Maj. Gen. Andrey Kolesnikov, of Russia’s 29th Army, the third of his rank—the equivalent of a U.S. brigadier general—to die in fighting since the invasion began.

Ukraine released no details on his death, which hasn’t been confirmed by Moscow. Western officials said they have confirmed all three deaths. The Russian Defense Ministry didn’t respond to a request for comment.

Firefighters extinguish a fire at a house after shelling in Kyiv.

Photo: aris messinis/Agence France-Presse/Getty Images

A Ukrainian serviceman walks toward the front line in Irpin, near Kyiv.

Photo: aris messinis/Agence France-Presse/Getty Images

Earlier this week, Ukraine released drone footage of a column of Russian armored vehicles being destroyed as it made its way through a suburb of Kyiv.

Western officials suggested the relative lull in the Russian offensive around the capital was to lay low and reposition forces for a new push. The U.K.’s Defense Ministry said it is concerned Russia was trying to reset for a renewed attack in coming days, including an offensive against Kyiv.

A large Russian military convoy seen northwest of Kyiv has largely dispersed and redeployed, according to Maxar Technologies, which has been tracking the convoy with satellite images. Maxar said it documented armored units maneuvering through towns near Antonov Airport, northwest of Kyiv. Maxar said the images show some convoy elements repositioned near the town of Lubyanka, outside of Kyiv, with towed artillery howitzers in firing positions nearby.

About 100,000 Ukrainians have joined the Territorial Defense Forces, the country’s volunteer force organized to resist the Russian invasion, Prime Minister Denys Shmyhal said on Friday. He also said 215,000 Ukrainians have returned home to help defend their country.

“What is going on in Ukraine is the liberation war of Ukrainians against the Russian invasion. In Ukraine, no one is waiting for Russians with flowers,” he said, speaking via a video link to a diplomatic conference in Turkey.

Still, Russian forces have made advances along Ukraine’s Black Sea coast, encircling the city of Mariupol. The daily bombardment of Mariupol, in which a maternity hospital was hit, has left the city of more than 400,000 without food, clean water or electricity.

Civilians before taking part in a military training exercise in Ivano-Frankovsk, Ukraine.

Photo: Alexey Furman/Bloomberg News

Russia’s invasion has triggered the fastest-growing refugee crisis since World War II. The number of people fleeing the war has reached 2.5 million, the United Nations refugee agency said Friday. Another two million people are displaced inside Ukraine, U.N. High Commissioner for Refugees Filippo Grandi said in a Twitter post.

In Moscow, the Kremlin signaled plans to move more forces toward its western border, and funnel what it described as volunteers from the Middle East to fight in Ukraine. Russia has been recruiting Syrians skilled in urban combat as its invasion is poised to expand deeper into Ukrainian cities.

Western officials are worried that Moscow will resort to deploying chemical, biological or nuclear weapons after struggling to make headway in the war.

Russia took its claims of U.S.-funded chemical and biological weapons work in Ukraine to the U.N. on Friday, calling a special meeting of the Security Council. Washington and Kyiv have repeatedly denied the claims and have warned that Moscow could be sowing disinformation to serve as a pretext for Moscow to use such weapons itself.

“I’m not going to speak about the intelligence, but Russia would pay a severe price if they use chemical weapons,” Mr. Biden said at the White House on Friday.

A cultural center and an administrative building following Russia’s aerial bombing in Byshiv, near Kyiv.

Photo: THOMAS PETER/REUTERS

Write to Alan Cullison at alan.cullison@wsj.com