Armenian forces killed have an Azerbaijani soldier as clashes festered along the volatile frontline of the breakaway Nagorny Karabakh region, a military spokesman in Baku said on Friday.

"On March 26 (Thursday) Armenians violated a ceasefire on the eastern sector of the Karabakh frontline," an Azerbaijani Defence Ministry official told AFP.

"An Azerbaijani serviceman was killed in action," the official said without giving further details.

The incident comes after three Armenian troops were shot dead in a similar clash last week, and takes the number of people reported killed on both sides this year to 22.

Baku and Yerevan have been locked in a dispute over Azerbaijan's Nagorny Karabakh region since a bloody war in the early 1990s and frequent flare-ups happen along the line dividing the warring sides.

Threatening a shaky 1994 truce, clashes between Azerbaijani and Armenian forces intensified again in January following an unprecedented spiral of violence last year.

Yerevan-backed ethnic Armenian separatists seized control of Karabakh and another seven adjacent districts of Azerbaijan during the conflict that left some 30,000 dead.

Despite years of negotiations, the two sides have not signed a final peace deal, with Armenian-populated Karabakh still internationally recognised as part of Azerbaijan.

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

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

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