Ukraine's capital Kyiv came under Russian bombardment overnight, with images released by the country's State Emergency Service on Tuesday showing a high-rise apartment block in flames after being struck.
Four people were confirmed dead, Kyiv mayor Vitali Klitschko said.
Firefighters tried to douse the flames and rescue workers helped to evacuate residents trapped in the building, using mobile ladders.
Emergency services said earlier that two people were killed when a residential building was attacked. It was not immediately clear if it was the same block.
In another part of the city, Reuters witnesses saw residents clearing debris from their homes after shelling blew out windows, ruined balconies and left wreckage strewn across the ground.
Klitschko on Tuesday morning announced a 35-hour curfew in the capital from Tuesday evening to Thursday morning.
Russia's defense ministry spokesperson Igor Konashenkov on Tuesday said Russian forces had taken full control of all territory in Ukraine's southern Kherson region, Russian news agencies reported.
Dnipro regional governor Valentyn Reznichenko said that Russian forces had fired rockets at the main civilian airport, destroying its runway and damaging the terminal building.
In addition, Russian forces shot down six Bayraktar TB-2 drones in the last 24 hours, the Interfax news agency reported, citing the ministry.
Reuters could not independently verify the reports.
Oleksiy Arestovich, an adviser to the Ukrainian president's chief of staff, said late on Monday that the war in Ukraine is likely to be over by early May when Russia runs out of resources to attack its neighbor.
Talks between Kyiv and Moscow - in which Arestovich is not personally involved - have so far produced very few results other than several humanitarian corridors out of besieged Ukrainian cities.
In a video published by several Ukrainian media outlets, Arestovich said the exact timing would depend on how much resources the Kremlin was willing to commit to the campaign.
"I think that no later than in May, early May, we should have a peace agreement – maybe much earlier, we will see; I am talking about the latest possible dates," Arestovich said.
"We are at a fork in the road now: There will either be a peace deal struck very quickly, within a week or two, with troop withdrawal and everything, or there will be an attempt to scrape together some, say, Syrians for a round two – and, when we grind them too, an agreement by mid-April or late April."
A "completely crazy" scenario could also involve Russia sending fresh conscripts after a month of training, he said.
Still, even once peace is agreed, small tactical clashes could remain possible for a year, according to Arestovich, although Ukraine insists on the complete removal of Russian troops from its territory.
Zelensky: Russian losses are mounting
Ukraine continues to resist Russian forces as the invasion continues into its 20th day. Negotiations are set to resume and martial law could be extended by 30 days.
Air raid sirens went off in several cities in Ukraine throughout the night, according to the Ukrainian news outlet EMPR.
So far, Ukrainian troops have continued to hold out as the Russian advance remains slow. However, fighting remains in many key cities, such as in the Black Sea port of Mariupol, which remains blockaded and under heavy fire by Russian forces as resources remain lacking. Humanitarian aid has been sent to the city, but the blockade has kept it stuck in nearby Berdyansk for three days now.
According to Ukraine's President Volodymyr Zelensky, Russian losses in the ongoing invasion have exceeded the casualties in two years worth of fighting in Chechnya.
These remarks came in his nightly video address, embedded below.
The transcript of his speech was shared by the Ukrainian state media outlet Ukrinform.
As Ukraine continues to fight back against Russian forces, reports have circulated of Ukrainian forces obtaining Russian equipment and vehicles. According to Zelensky, this has gone on to such an extent that Russia is now essentially a supplier of military equipment for the Ukrainian army.
"They flee the battlefield, throwing away equipment," Zelensky said. "We take them as trophies and use them to defend Ukraine."
The president further stated that the Russian military will face justice and take responsibility for what he described as war crimes, singling out the situation in a number of cities such as Mariupol, Kharkiv, Sumy, Irpen and Chernihiv.
There is still a danger that Russian naval troops could attempt to land on Ukraine's Black Sea coast, but according to Odessa Regional Military Administration head Maxim Marchenko, the army is ready.
"Our military is ready for this," he said on Telegram, according to Ukrainian state media Ukrinform. "All the enemy will see is the bottom of the Black Sea."
Negotiations and martial law
Zelensky said that negotiations between Ukraine and Russia are set to resume on Tuesday in an effort to bring an end to the ongoing conflict in Ukraine.
"Our delegation also worked on this in negotiations with the Russian party," Zelensky said in his nightly video address. "Pretty good, as I was told. But let's see. They will continue tomorrow."
This comes after the president requested the government extend martial law in the country for another 30 days in light of the ongoing Russian invasion.
Ukraine plans to open nine "humanitarian corridors" on Tuesday to evacuate civilians from areas besieged by Russian forces and will try to deliver humanitarian supplies to encircled Mariupol, Deputy Prime Minister Iryna Vereshchuk said.
Hundreds of thousands of residents of Mariupol, which has been under constant bombardment, have sheltered in basements and the ruins of buildings without water or power for more than a week. Moscow on Monday allowed the first convoy to escape.
"In the first two hours, 160 cars left," Andrei Rempel, a representative of the Mariupol City Council, told Reuters.
Vitaliy Koval, governor of the northern region of Rivne, said separately that the death toll from a Russian air strike on a television tower in his region on Monday had risen to at least 19.
A bill was submitted Monday to the Verkhovna Rada, Ukraine's legislature, to approve the extension, and information about it was shared on its Telegram channel.
A copy of the bill itself is available on the Verkhovna Rada's website and can be seen here.
Reuters contributed to this report.
This is a developing story.