Russian strikes hit residential areas in the Ukrainian capital Kyiv early Tuesday, killing at least four people, emergency services said.
Two large blasts echoed across the center of the city just before dawn on Tuesday. Late on Monday, tracer bullets flashed across the night sky as Ukrainian forces apparently targeted an enemy drone.
"Today is a difficult and dangerous moment," Kyiv's Mayor Vitali Klitschko said.
"The capital is the heart of Ukraine, and it will be defended. Kyiv, which is currently the symbol and forward operating base of Europe's freedom and security, will not be given up by us."
He called on men who took wives and children to the relative safety of the west of the country earlier in the conflict to return to the capital to fight. Some have done so already, he and his brother Wladimir told Reuters in a recent interview.
Two bodies had previously been removed from the rubble after a strike on a 16-story building in the Sviatoshynskyi district, the emergency service said in a Facebook post, adding that 27 people had been rescued from the site.
Another residential building in the Podilsk area also came under attack, it said.
"A fire started on the first five floors of a ten-story residential building on Mostytska street as a result of ammunition fire," it said.
Agence France-Presse (AFP) journalists said they heard at least three powerful explosions in the center of Kyiv early on Tuesday morning.
In Podilsk, smoke was still billowing from the blackened impact site in the middle of the building, said an AFP journalist at the scene.
Shattered glass and debris were spread around the explosion site while residents were throwing charred wreckage out of their windows.
Windows were blown out by the impact from surrounding blocks.
Separately, the emergency service said a private home was hit in the Osokorky district in southeastern Kyiv.
Images shared by the emergency service showed the blackened wall of a two-story building with smoke seeping from the shattered windows.
35-hour curfew after increased shelling
A curfew will be imposed on the Ukrainian capital Kyiv from 8 p.m. (6:00 p.m. GMT) on Tuesday to 7 a.m. (5:00 a.m. GMT) on Thursday after several apartment blocks were struck by Russian forces based outside the city, Mayor Vitaliy Klitschko announced.
Two people were killed in the latest bloodshed, he said.
"It is prohibited to move around the city without special permission, except to go to bomb shelters," Klitschko said. "The capital is the heart of Ukraine, and it will be defended. Kyiv, which is currently the symbol and forward operating base of Europe’s freedom and security, will not be given up by us."
Fighting has intensified in recent days around Kyiv, which is almost completely surrounded by Russian forces that invaded Ukraine on Feb. 24.
More than half of Kyiv's 3 million inhabitants have fled the city since the start of the Russian offensive.
Fierce fighting has been going on for several days between Russian and Ukrainian forces on the northwest outskirts of Kyiv.