A Frenchman was killed "in fighting" in Ukraine, the French Foreign Ministry announced on Friday, 100 days after the start of the Russian invasion.

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"We learned the sad news that a Frenchman had been mortally wounded in fighting in Ukraine," the Quai d'Orsay said in a written response. "We extend our condolences to his family."

According to a security source interviewed by AFP, the man was "a fighter who left as a volunteer".

The identity of this man has not been communicated, nor the place where he perished.

French radio Europe 1 reported on Thursday of a "first French fighter" killed in Ukraine, "mortally wounded by artillery fire" in the Kharkiv region (northeast).

"The young man had joined the Ukrainian International Defense Legion and participated in the fighting against the Russian army", according to Europe 1.

Britain reported the death of one of its nationals and the disappearance of another at the end of April.

According to British media, the slain was a veteran of the British army. His former comrades had paid tribute to him on a Facebook page and a fundraising page had been set up.

According to British media, the two nationals were fighting against Russian forces as volunteers.

The war in Ukraine entered its 100th day on Friday. Shortly after Russia invaded his country on February 24, Ukrainian President Volodymyr Zelensky called for the formation of an “international legion” of foreign volunteers to help him defend Ukraine.

“Victory will be ours,” Mr. Zelensky said on Friday, after admitting the day before that Russian troops currently occupied “about 20%” of the country.

The Kremlin, for its part, claims to have achieved “some” of the objectives of its invasion supposed to “denazify” Ukraine and protect its Russian-speaking population and intends “to continue until all the objectives of the special military operation are fulfilled”.

"Ukraine, in its entire territory, is a war zone," insisted the Quai d'Orsay in its written response. "In this context, it is strictly advised not to travel to Ukraine, whatever the reason."