Russia has recognized that it has suffered a "significant loss" of troops. Its operation on Ukraine has not moved as rapidly as the Kremlin desired, more than a month after President Vladimir Putin began the invasion.

"We have suffered severe military losses. Despite Ukraine's persistent opposition, it's a great disaster for us," Kremlin spokesman Dmitry Peskov told Sky News on Thursday.

Although Moscow has not provided an exact figure, Ukrainian authorities believe that at least 18,900 Russian soldiers have been killed in combat since the invasion began on 24 February.

Moscow's unwarranted attack has displaced over four million people and resulted in the death or injury of thousands.

Vadym Boichenko, the mayor of Mariupol's southern port city, stated that the town had lost almost 5,000 inhabitants, including 210 children.

Ukraine said that between 150 and 300 individuals might be buried in a mass grave outside a church where Mr. Putin's men allegedly massacred civilians in Bucha, near the capital Kyiv.

Russia has been charged with war crimes in connection with the Bucha massacre, and the west has imposed further restrictions, notably on Mr. Putin's daughters.

Mr. Peskov rejected ideas that the Russian president might go before a war crimes court, saying: "We see no possibility of that, we do not believe it is realistic."

Following the Bucha massacres, the United Nations General Assembly suspended Russia from the UN Human Rights Council, citing "grave concern about the deteriorating human rights and humanitarian situation."

Russia responded by resigning from the council.

Moscow has denied attacking civilians and claimed that photographs of bodies in Bucha were fabricated to justify additional sanctions and hinder peace discussions.

"Ukraine has a long track record of successfully investigating war crimes committed by some Ukrainian troops following the opening stages of the war in 2014-2015, and these offenses have been examined. "Those individuals were brought to court and sentenced," Mr. Peskov said in a rebuttal to Ukraine.

The war-torn nation has urged friends to halt purchases of Russian oil and gas and bolster its military capabilities in the face of European differences.

Volodymyr Zelensky, Ukraine's president, said in a nightly speech to the nation on Thursday: "Ukraine requires weapons that will enable it to win on the battlefield, and that will be the strongest possible sanction against Russia."

He stated that the situation in Borodyanka, some 15 miles from Bucha, was "significantly more heinous."

UN humanitarian director Martin Griffiths expressed pessimism on Thursday about achieving a truce to halt bloodshed as Russia shifted its focus to eastern Ukraine's Donbas area.

"I believe it will be difficult since the two sides, as I now know, have minimal trust in one another. "I am pessimistic," remarked the undersecretary-general.