Armenian Prime Minister Nikol Pashinyan led Saturday a thousands-strong march in memory of those killed in clashes with Azerbaijan as the Caucasus country began three days of mourning amid persisting tensions.

Separatist officials in the breakaway region of Nagorno-Karabakh said Saturday that three fighters were wounded in a skirmish with Azerbaijani forces, undermining a recent peace deal brokered by Russia.

The defence ministry in the ethnically Armenian province said in a statement that Azerbaijani troops attacked Friday evening and that "three Armenian servicemen were injured during the ensuing gunfight". 

Azerbaijan said Thursday that nearly 2,800 of its soldiers were killed in recent fighting over Nagorno-Karabakh, the first details it has released of military losses in weeks of clashes with Armenian forces.

Azerbaijani soldiers and military trucks rolled into the district of Kalbajar on Wednesday, reclaiming the second of three regions Armenia is handing back under a deal that ended weeks of fighting.

Armenian Prime Minister Nikol Pashinyan called Saturday for greater military cooperation with Russia, a day after Azerbaijani troops began moving into territory in Nagorno-Karabakh previously held by Armenian separatist forces.

Armenia and Azerbaijan agreed on a deal with Russia to end weeks of fierce clashes over Nagorno-Karabakh on Tuesday, after a string of Azerbaijani victories in its fight to retake the disputed region.

Three civilians were killed as Azerbaijani forces shelled the main city of the disputed Nagorno-Karabakh region on Friday, Armenia said, following weeks of fighting over the mountainous province.

A third attempt at halting weeks of fighting over Nagorno-Karabakh collapsed quickly on Monday with Armenia and Azerbaijan trading accusations of violating the US-brokered ceasefire within minutes.

US Secretary of State Mike Pompeo on Friday urged an end to  fighting over Nagorno-Karabakh as he met his counterparts from Azerbaijan and Armenia but there were no signs of progress.

The foreign ministers of Armenia and Azerbaijan were in Moscow on Wednesday for meetings with Russia's top diplomat Sergei Lavrov as world powers seek to halt fighting over Nagorno-Karabakh.

The ministers were visiting the Russian capital, their respective ministries said as the pair are due to meet with US Secretary of State Mike Pompeo on Friday.