- Zelenskyy said Ukraine's "worst situation" is in Mariupol, where scores of civilians may be dead.
- The besieged southern port city has been the target of a devastating Russian shelling campaign.
- Mariupol's city council recently accused Russia of using mobile crematoriums to burn bodies.
Ukrainian President Volodymyr Zelenskyy said on Monday that "tens of thousands" of Ukrainian civilians could be dead in the besieged southern port city of Mariupol.
Zelenskyy said in a video address to South Korean lawmakers, which he later posted to Telegram, that Ukraine's "worst situation" is in Mariupol, the bombarded city that has been surrounded by Russian troops for weeks.
"Mariupol is destroyed — there are tens of thousands of dead," Zelenskyy said. "But even despite this, the Russians did not stop their offensive. They want to make Mariupol a demonstratively destroyed city."
He added: "The occupiers blocked it and did not even allow food and water to be brought there. They tried to capture it in the most brutal way — just to destroy everything in the city."
Russian forces have shelled Mariupol in a devastating campaign, hitting a school, maternity hospital, and even a theater marked as a shelter with children inside. Ukraine has said that creating humanitarian corridors and evacuating civilians has proved a difficult feat.
It's not immediately clear exactly how many civilians have died there — Mariupol's city council said in a conservative estimate last week that around 5,000 civilians were killed.
"Given the size of the city, catastrophic destruction, the duration of the blockade, and fierce resistance, tens of thousands of civilians from Mariupol could fall victim to the invaders," city council warned, matching Zelenskyy's tally on Monday.
The United Nations on Monday said it has recorded 1,793 civilian deaths in Ukraine since Russia invaded the eastern European country on February 24, but said that "the actual figures are considerably higher."
"The receipt of information from some locations where intense hostilities have been going on has been delayed and many reports are still pending corroboration," it said in a report, citing Mariupol as one location with "allegations of numerous civilian casualties."
Mariupol's city council has also accused Russia of orchestrating the use of mobile crematoriums to destroy bodies of dead civilians and hide evidence of possible war crimes.
UK intelligence warned on Monday that Russian forces could also soon use phosphorus munitions— which causes severe burns — in the city.
Meanwhile, Zelenskyy and Western officials are preparing for Russia to reposition its forces to focus on Ukraine's eastern Donbas region after failing to capture the capital city Kyiv in more than six weeks of war.
NATO Secretary-General Jens Stoltenberg said, however, that Russian President Vladimir Putin still wants to capture all of Ukraine, despite the latest troop movement.