Azerbaijan has accused Armenia of shelling its positions near the disputed enclave of Nagorno-Karabakh, which the two neighbours have been fighting over intermittently for 30 years, Tass news agency says.
The Azeri defence ministry said it had returned fire after Armenia used artillery to attack troops in the Lachin and Kalbajar regions to the west of the enclave.
Separately, Armenia's defence ministry denied the charge, Interfax news agency said.
The dispute over the region, a mountainous territory inside Azerbaijan controlled since the 1990s by ethnic Armenians, flared in 2020 into a six-week war in which Azeri troops regained swathes of territory.
The two sides agreed to work on a peace plan after Russia brokered a ceasefire but periodically accuse each other of firing shells across the border.
US Secretary of State Antony Blinken spoke separately with the leaders of Armenia and Azerbaijan on Monday to try to nudge the former Soviet republics toward peace.