Armenia reports deaths in Azerbaijan border clashes
The six-week armed conflict for control of the disputed Nagorno-Karabakh region claimed more than 6,500 lives and ended last November with a Russian-brokered truce.
Under the ceasefire agreement, Armenia ceded swathes of territories it had controlled for decades.
"There are fatalities and wounded among Armenian troops as a result of fighting that erupted following an attack by Azerbaijani forces," Armenia's defence ministry said on Tuesday.
It said the number of casualties was being verified and that Yerevan had "lost control of two military positions".
Earlier on Tuesday, the two sides accused each other of initiating fighting along their shared border.
Armenia appealed to ally Russia for military support in protecting its territorial integrity, according to their military pact.
Since last year's war, both Armenia and Azerbaijan have reported occasional exchanges of fire, sparking fears of another flare-up in their territorial dispute.
Ethnic Armenian separatists in Nagorno-Karabakh broke away from Azerbaijan as the Soviet Union collapsed in 1991, and the ensuing conflict claimed around 30,000 lives.