"We have achieved victories and more are to come," boasted Denis Pushilin, a leader of the self-declared "People's Republic of Donetsk" at a rally in the main city in Ukraine's eastern industrial belt.
But he added: "We need strong men to protect our republic because civil war is raging in our region.
"Many men are falling every day, so we need more."
He gave no specific figures on the number of casualties among rebel ranks, although fighting is reported almost every night around insurgent flashpoints such as Slavyansk.
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Pushilin was addressing a crowd of a few hundred people gathered around a huge granite statue of Lenin in the centre of the city of one million.
Pro-Russian rebels in Donetsk and the neighbouring region of Lugansk declared their own sovereign republics after claiming victory in independence referendums on May 11 that were denounced as illegal in Kiev and the West.
The separatists in Donetsk have since set up their own parliament and a government headed by a shadowy Russian "consultant" called Aleksandr Borodai, and appealed to join the Russian Federation.
"If men are not willing then we have no other option than to call up women and take them into the militias," he said.
"I would have expected there would have been at least 1,000 men willing to risk their lives not just in their home towns but on the frontlines," he added, complaining that many came simply to demand weapons for protection at home.