"Tomorrow, we will receive officers from France. They are specialists ready to fight with us," Alexandre Zakhartchenko said at a Sunday press conference.
However, he gave no details on the French servicemen, nor did he specify their numbers.
There are also "Serbs and Swiss" among the pro-Moscow militants who are fighting for "European and socialist ideals", Zakhartchenko claimed.
He also said the separatists had launched an offensive against Ukrainian forces in the south of Donetsk - the largest rebel-held city in Ukraine that has seen intense fighting in recent weeks.
Zakhartchenko said hundreds of soldiers loyal to Kiev had been killed or injured in battles around the city. None of his claims could be independently verified.
Captured soldiers paraded through Donetsk
On Sunday Pro-Russian rebels in eastern Ukraine paraded dozens of captured soldiers before a jeering crowd on Sunday in mockery of Independence Day celebrations in the capital.
Ukraine's pro-Western government had sought to boost morale with an upbeat military parade to mark the country's independence from the Soviet Union in 1991.
Speaking to a crowd of thousands in the iconic Independence Square, known locally as the Maidan, President Petro Poroshenko decried Russian "aggression" and said he was "convinced that the battle for Ukraine, for independence, will be our success".
But it was a markedly different scene in the eastern rebel stronghold of Donetsk, where around 40 or 50 captured government soldiers were paraded through the city's central Lenin Square as onlookers hurled garbage and empty bottles at them.
"You are killing children!" screamed some in the crowd at the prisoners, who walked with heads bowed and their hands behind their backs before being placed on two buses and taken to an unknown destination.
The grim scene appeared designed to recall the famous moment in 1944 when thousands of captured Nazi soldiers were paraded through Moscow on Stalin's orders.
Human Rights Watch deputy director Rachel Denber said on Twitter that the event amounted to "humiliating and degrading treatment" of prisoners and was therefore in breach of the Geneva Convention.