MOSCOW (AP) — Russian officials said a large fire was blazing Friday at a prison in Siberia where inmates and guards have clashed.

There was no official information about casualties or damage at the prison in Angarsk, 4,000 kilometers (2,500 miles) east of Moscow.

But Pavel Glushenko, a local human rights activist, said on social media that “full-scale hostilities” were taking place at the maximum-security prison.

Details were unclear about what set off the clashes, with reports either that prisoners attacked guards or that a guard beat a prisoner.

The prison holds about 1,200 inmates.