Ukrainian Defense Minister Stepan Poltorak has said that 42,500 separatists and Russian soldiers are stationed in eastern Ukraine, where government forces have been battling pro-Russian rebels since April 2014.
"They have 558 tanks, combat vehicles, artillery systems, and other weapons,” Poltorak told a meeting of the Ukraine-NATO Interparliamentary Council in Kyiv on June 8.
Ukrainian President Petro Poroshenko said last week that more than 9,000 Russian servicemen are operating on Ukrainian territory.
Kyiv and the West accuse Russia of backing the rebels, a charge Moscow denies.
According to Poltorak, more than 100 Ukrainian personnel and more than 50 civilians have been killed since a cease-fire agreement was signed in Minsk in February.
He also said that some 24,000 Russian servicemen are stationed in Ukraine's Crimean Peninsula, which was annexed by Russia in March 2014.