"Armenian forces have yet again violated the ceasefire and killed an Azerbaijan army warrant officer," Azerbaijan's defense ministry said in a statement without giving further details.

His death takes to at least 26 the number of people reported killed this year on both sides.

Yerevan-backed ethnic Armenian separatists seized control of Karabakh and several other regions of Azerbaijan during the conflict that left some 30,000 dead.

Despite years of negotiations, the two countries have not signed a final peace deal following a shaky 1994 truce.

The predominantly Armenian-populated region is internationally recognized as part of Azerbaijan.

Karabakh's ethnic-Azeri community around a quarter of the population before the war was driven out.

Baku, who's military spending exceeds Armenia's entire state budget, has threatened to take back the territory by force if negotiations fail to yield results.

Armenia, backed militarily by Russia, says it could crush any offensive.

Threatening a shaky 1994 truce, the clashes between Azerbaijani and Armenian forces across their shared border and along the Karabakh frontline intensified last year.