Ukraine's President Volodymyr Zelensky said late on Monday that Kyiv was ready for an exchange of prisoners with Russia "even tomorrow" and called on his allies to put pressure on Moscow.

"The exchange of people - this is a humanitarian matter today and a very political decision that depends on the support of many states," Zelensky said in a question-and-answer video link with audience at the World Economic Forum in Davos.

"It is important ... to pressure politically on any level, through powerful business, through the closure of businesses, oil embargo ... and through these threats actively intensify the exchange of our people for Russian servicemen." "We do not need the Russian servicemen, we only need ours," Zelensky said.

"We are ready for an exchange even tomorrow." Zelensky said that Ukraine has involved the United Nations, Switzerland, Israel and "many, many countries", but the process was very complicated.

Ukraine urges more world pressure, says it repels Russian attack on eastern city

Several thousand people are in captivity after Russia captured the port city of Mariupol in southeastern Ukraine and as a result of the battle in the eastern Donbas region, he said.

Russia sent thousands of troops into Ukraine on Feb. 24 for a what it calls a "special operation" to demilitarise its neighbour and root out dangerous nationalists - claims dismissed by Kyiv and Western countries as false pretexts for a land grab.

In recent weeks, Russian forces have been trying to encircle Ukrainian forces and fully capture the Luhansk and Donetsk provinces that make up the Donbas region, where Moscow backs separatist fighters.