Armenia said Tuesday that at least 49 of its troops were killed in clashes with Azerbaijan, the worst fighting between the arch foes since their 2020 war over the disputed Nagorno-Karabakh region.

"For the moment, we have 49 (troops) killed and unfortunately it's not the final figure," Prime Minister Nikol Pashinyan told parliament in the Armenian capital Yerevan.

He said the intensity of fighting had subsided following heavy shelling from Azerbaijan that began overnight.

Earlier on Tuesday Armenia appealed to world leaders for help, saying that Azerbaijani forces were trying to advance onto its territory.

Azerbaijan's defence ministry said its forces were responding to Armenian provocation and denied claims that they were hitting civilian infrastructure.

It said the clashes took the lives of some of its troops, without giving the number of casualties.

The neighbours fought two wars -- in the 1990s and in 2020 -- over Nagorno-Karabakh, an Armenian-populated enclave of Azerbaijan.

Six weeks of fighting in the autumn of 2020 claimed more than 6,500 lives and ended with a Russian-brokered ceasefire.

Under the deal, Armenia ceded swathes of territory it had controlled for decades and Moscow deployed about 2,000 Russian peacekeepers to oversee the fragile truce.

Ethnic Armenian separatists in Nagorno-Karabakh first broke away from Azerbaijan when the Soviet Union collapsed in 1991. The ensuing conflict claimed around 30,000 lives.