An exchange of fire along the border between Armenia and Azerbaijan in the disputed Nagorno-Karabakh region in the Caucasus left at least five dead on Sunday, officials said.

The countries have fought two wars that claimed thousands of lives for the control of Azerbaijan's Armenian-populated enclave of Karabakh.

"A sabotage group of the Azerbaijani armed forces opened fire on the car of a Passport and Visa Department of the police... three police officers were killed," pro-Armenian separatist authorities said Sunday.

Azerbaijan's defence ministry denied that version, saying its forces were trying to stop vehicles carrying weapons when "Azerbaijani servicemen were fired at, as a result of the exchange of fire on both sides there are dead and wounded."

It later said that two of its servicemen "became martyrs".

Armenia's foreign ministry said Azerbaijan's version was "absurd" and resulted from a "provocation planned in avance and instructed by the top leadership".

There has been a fragile truce between the neighbours since a 2020 war that left more than 6,500 dead and forced Armenia to cede territories it had controlled for decades.

The part of Karabakh that still remains under Armenian separatist control is guarded by Russian peacekeepers.

Since mid-December, a group of self-styled Azerbaijani environmental activists has barred the only road linking Karabakh to Armenia, the Lachin corridor, to protest what they say is illegal mining.

Yerevan has accused Baku of creating a blockade there.

Following Sunday's clashes Armenia said "sending an international fact-finding team to the Lachin corridor and Nagorno-Karabakh is becoming a vital necessity".

Azerbaijan's ministry of defence said, "Today's incident once again shows that Azerbaijan needs to create an appropriate checkpoint on the Lachin-Khankendi road."