Russian peacekeepers have been on the ground in Nagoro-Karabakh in a bid to get a Moscow-brokered ceasefire to hold. Armenia is yet to comment on the claims.

Azerbaijan’s Defense Ministry said on Monday that its army units had been attacked by "an illegal Armenian armed group"in Nagorno-Karabakh. 

"As a result of the attack, a soldier of the Azerbaijan army … was killed," the ministry said on Monday, noting that another serviceman was wounded but in stable condition.

Azerbaijan officials said they thwarted the attack, leaving all six attackers dead.

The Defense Ministry vowed to take "decisive measures" if repeat attacks were carried out by Armenian troops.

It comes after the Armenian Defense Ministry denied media reports of fighting in the neighbouring Hadrut region.

Neither Armenian nor Nagorno-Karabakh officials have so far commented on Azerbaijan’s statement.

What is the Nagorno-Karabakh conflict?

Nagorno-Karabakh lies within Azerbaijan but was under the control of ethnic Armenian forces backed by Armenia since a war there led to a ceasefire in 1994.

That war left Nagorno-Karabakh itself and substantial surrounding territory in Armenian hands.

Heavy fighting erupted in late September in the biggest escalation of the decades-old conflict between Armenia and Azerbaijan, killing more than 5,600 people on both sides.

Dozens of civilians on both sides died, as well as hundreds of soldiers.

Russia brokers a peace deal

A Russian-brokered peace dealthat saw Azerbaijan reclaim much of the breakaway region along with surrounding areas ended six weeks of fierce fighting on November 10.

On December 12, Armenia and Azerbaijan reported new clashes in the south of Nagorno-Karabakh, accusing each other of breaching the ceasefire.

Russian peacekeepers deployed to monitor the peace deal also reported a violation but did not assign blame.

The Russian peacekeeping force of approximately 2,000 soldiers reported earlier this month that one Russian soldier died during a mine-clearing operation but says the peace deal is largely holding.

Nagorno-Karabakh’s declaration of autonomy has not been recognized by any country, including Armenia.

Tens of thousands of opposition supporters took to the streets of Armenia earlier this month, calling on their prime minister to resign.