Four Armenian separatist fighters were killed Wednesday in the breakaway Nagorno-Karabakh region by Azerbaijani fire, rebels said, as Baku and Yerevan held peace talks mediated by the United States.

Armenia and Azerbaijan have been locked in a decades-long conflict for control of the mountainous region in Azerbaijan, which is populated mainly by ethnic Armenians.

The clashes erupted one day after the United States opened three days of peace talks between the Caucasus arch foes, in its latest attempt to quell a conflict that has flared repeatedly.

On Wednesday morning, "units of the Azerbaijani armed forces opened fire with artillery" on Armenian positions, Karabakh's defence ministry said.

"Four servicemen were killed in action as a result of another provocation by Azerbaijan," it said, adding later in another statement that the situation along the border was now "relatively stable".

There have been frequent clashes along Armenian-Azerbaijani border, despite the two former Soviet republics negotiating a peace agreement under the mediation from the European Union and United States. 

On Tuesday, Azerbaijan's defence ministry said "illegal Armenian armed detachments in the territory of Azerbaijan... opened fire at the Azerbaijan Army positions," wounding one Azerbaijani serviceman. 

The same day, US Secretary of State Antony Blinken opened closed-door negotiations with Armenia's Foreign Minister Ararat Mirzoyan and his Azerbaijani counterpart Jeyhun Bayramov just outside Washington -- the second round of such talks he has led in as many months. 

- 'Ethnic cleansing' -

Earlier this month, Armenian Prime Minister Nikol Pashinyan accused Baku of pursuing a policy of "ethnic cleansing" in Karabakh, saying traffic is being blocked through the Lachin corridor -- the sole road linking the territory with Armenia. 

The blockade followed a months-long roadblock by Azerbaijani environmental activists, which Yerevan claims has lead to a humanitarian crisis in the mountainous enclave that had experienced shortages of food and fuel. 

Azerbaijan has insisted that civilians and aid convoys can travel through. 

But the International Committee of the Red Cross said Azerbaijan had blocked access for convoys delivering aid to Karabakh, raising concerns of shortages of food and medicine. 

Russia has historically been the mediator between the two former Soviet republics, but Brussels and Washington have been increasingly active as Moscow gets bogged down in its invasion of Ukraine. 

Armenia has repeatedly accused Russian peacekeepers of failing to live up to promises to protect ethnic Armenians in line with a 2020 truce negotiated by Moscow after six weeks of fighting left thousands dead.

The ceasefire agreement saw Armenia cede swathes of territories it had controlled for decades.  

When the Soviet Union collapsed in 1991, ethnic Armenian separatists in Karabakh broke away from Azerbaijan. The ensuing conflict claimed some 30,000 lives.

mkh-im/jbr/rox