Moscow on Monday expressed "serious concern" over fresh tensions between Armenia and Azerbaijan and said any unilateral moves in violation of ceasefire agreements were unacceptable.

The comments came a day after Azerbaijan said it had set up a checkpoint on the only land link to the contested region of Nagorno-Karabakh, sparking an angry response from Armenia.

Armenia and Azerbaijan have fought two wars over Karabakh.

"We express our serious concern about the situation within the zone of responsibility of Russian peacekeepers in Nagorno-Karabakh," the Russian foreign ministry said.

"We call on the parties to immediately return to the existing agreements," the ministry said in a statement.