Baku (AFP) - Azerbaijan has destroyed an Armenian air defence system in the breakaway Nagorny Karabakh region, officials in Baku said Tuesday, as separatist authorities vowed retaliation, raising tensions in the festering conflict.

Ex-Soviet Azerbaijan and Armenia are locked in a protracted conflict over the disputed region, and frequent exchanges of fire nearly spiralled into all-out war last year.

"Azerbaijani forces destroyed on Monday an Armenian Osa air defence system and its crew in the Fisuli-Khojavend sector of Karabakh's frontline in order to avert the threat it posed to Azerbaijan's aircraft," an official from the press service of Azerbaijan's defence ministry told AFP.

The separatist defence ministry in Karabakh said in a statement that the Azerbaijani army had damaged its military equipment with a guided missile, but denied casualties among its troops.

"Azerbaijani forces' provocation will not be left unanswered," it said.

The incident came after bloody clashes erupted between Azerbaijani and Karabakh troops in February that killed several Azerbaijani servicemen.

In April last year, at least 110 people from both sides were killed as simmering violence flared into the worst clashes in decades over the region.

A Russian-brokered ceasefire ended the four days of fierce fighting but attempts to relaunch the stalled peace process since then have failed.

Baku and Yerevan have feuded over the Nagorny Karabakh region since Armenian separatists seized the territory in a war that claimed some 30,000 lives in the early 1990s and ended in a frail 1994 truce.

The two sides never signed a firm peace deal.

Energy-rich Azerbaijan, whose military spending exceeds Armenia's entire state budget, has repeatedly threatened to take back the breakaway region by force.

But Moscow-allied Armenia has vowed to crush any military offensive.