Russia’s defence ministry said on Sunday it had killed more than 600 Ukrainian servicemen in a massive rocket strike on two buildings in eastern Ukraine temporarily housing Ukrainian forces.

Reuters could not immediately verify the defence ministry’s assertion. There was no immediate comment on the Russian claim from Ukraine, though the mayor of Kramatorsk, the eastern Ukrainian town Russia said it had targeted, said earlier on Sunday on Facebook that nobody had been killed in an attack on various buildings in the city.

Russia’s defence ministry said the strike on the buildings in Kramatorsk was revenge for a deadly Ukrainian attack earlier this year on a Russian barracks in Makiivka in part of the Donetsk region controlled by Moscow’s forces in which at least 89 servicemen were killed.

The ministry said in a statement that it had used what it called reliable intelligence to target the Ukrainian troops. It said more than 700 Ukrainian troops had been housed in one hostel and more than 600 in another.

“As a result of a massive missile strike on these temporary deployment points of Ukrainian army units, more than 600 Ukrainian servicemen were destroyed,” the defence ministry said.

If true, it would be the single largest loss of Ukrainian troops since Russia invaded on Feb. 24 last year.