Fighting between Armenian and Azerbaijani forces escalated on Tuesday, with Azerbaijan reporting seven more troops killed, including a general, and Armenia saying it has lost two servicemen.
Skirmishes on the volatile border between the two South Caucasus nations began on Sunday. The new losses bring the number of Azerbaijani troops killed to 11. Armenia previously reported five of its troops wounded.
The two neighbours in the South Caucasus have been locked in conflict over Nagorno-Karabakh, a region of Azerbaijan that has been under the control of ethnic Armenian forces backed by Armenia since a war there ended in 1994. International efforts to settle the conflict have stalled.
Armenian and Azerbaijani forces have frequently engaged in clashes. The current outburst of fighting appears to be the most serious spike in hostilities since 2016 when scores were killed in four days of fighting.
The latest incident began on Sunday when Armenian and Azerbaijani troops exchanged fire in the northern section of their border. Officials in both countries blamed each other for starting the fighting and said that sporadic shelling has continued.
Armenian Prime Minister Nikol Pashinyan on Monday accused Azerbaijan of provoking the clashes and warned that it would "bear responsibility for the unpredictable consequences".
Azerbaijani President Ilhan Aliyev denounced what he described as "another provocation of Armenia" and vowed to protect Azerbaijan's national territory.
Turkey, which has close ethnic and cultural ties with Azerbaijan, has voiced strong support to Baku in the conflict.
The United States and Russia, which co-chair the Minsk group of the Organization for Security and Cooperation in Europe that has tried to negotiate a settlement of the Nagorno-Karabakh conflict, have condemned the violence and called for restraint.