Ukraine has lost up to 13,000 soldiers since the beginning of Russia's nearly 10-month-long unprovoked war, presidential adviser Mykhailo Podolyak said.

Mr Podolyak, a senior adviser to president Volodymyr Zelensky, on Thursday said the number is between 10,000-13,000.

"We are open in talking about the number of dead," he told Kanal 24 channel, adding that more soldiers had been wounded than had died.

"We have official figures from the general staff, we have official figures from the top command, and they amount to (between) 10,000 and 12,500 to 13,000 killed," Mr Podolyak said.

His remarks were the first official estimate of the dead soldiers since late August when the head of the armed forces said nearly 9,000 military personnel had been killed.

Neither Ukaraine nor aggressor Russia has officially announced the toll of the soldiers killed in the war.

Mr Podolyak added that the president would make the official numbers public "when the right moment comes”.

Oleksiy Arestovych, one of Mr Zelenksy’s advisors, in an interview this week, claimed that the Russian death count was around seven times that of Ukraine.

On Wednesday, EU leader Ursula Von der Leyen reportedly pegged the number of Ukrainian troops killed at 100,000, which a spokesperson later clarified was a mistake and the figure referred to those both killed and injured.

Last month, top US general Mark Milley estimated that Russia's military had seen more than 100,000 of its soldiers killed and wounded in Ukraine. He suggested that Mr Zelensky's forces "probably" suffered a similar level of casualties.

The Ukrainian defence ministry in a tweet on Thursday claimed at least 89,440 Russian troops were "eliminated" since Vladimir Putin launched his occupation on 24 February.

Last week, the Russian president met with 17 mothers of soldiers fighting in Ukraine, telling those who had lost sons that he shared their sufferings.

Mr Putin met with the women at his Novo-Ogaryovo residence outside Moscow to mark Russian Mother’s Day and shared tea and cakes.

“I would like you to know that, that I personally, and the whole leadership of the country, we share your pain,” Mr Putin said in a video clip released from the meeting.

“We understand that nothing can replace the loss of a son - especially for a mother,” he added.

Meanwhile, US president Joe Biden said he would be willing to meet his Russian counterpart to learn whether he’s willing to end the war.

Mr Biden said he’d take a meeting with Mr Putin “if he’s willing to talk to find out what he’s willing to do”, speaking at a news conference alongside French president Emmanuel Macron.

“But I’ll only do it in consultation with my Nato allies. I’m not going to do it on my own,” he added.