President Vladimir Putin has signed a decree to make losses of Russian troops in peacetime a state secret.

The decree published on the official government website and signed by Putin on Thursday makes it a crime to publish information about peacetime losses of Russian troops in "special operations."

The decree comes as evidence of Russian involvement in the conflict in eastern Ukraine is mounting.

Ukraine last week captured two men who it said were Russian officers operating on the side of the separatists in eastern Ukraine. The Russian defence ministry said the two are no longer active servicemen. However, the men insisted in several video interviews they were in Ukraine on their commanders' orders.

The measure brought strong criticism from Amnesty International and the United States.

"Not only is this decree a blatant attack on freedom of expression, it also has sinister undertones that will intensify speculation President Putin has something to hide — specifically losses incurred by Russia's military in Ukraine," John Dalhuisen, Amnesty's Europe and Central Asia director, said in a statement.

U.S. State Department spokesman Jeff Rathke said in Washington, "We see this as a misplaced effort to cover up what everyone knows, and that is that Russian active-duty military personnel are fighting and dying in eastern Ukraine and that the Russian government is denying it."