Armenian and Azerbaijani forces on Tuesday engaged in new fighting over the disputed Nagorno-Karabakh region despite pleas from world and regional powers for them to observe a ceasefire agreed last week.

More than two weeks of conflict between the Caucasus rivals has left almost 600 dead, including 73 civilians, according to a tally based on partial tolls from both sides.

The Nagorno-Karabakh region of Azerbaijan, overwhelmingly populated by Armenians, has been controlled by Armenians since a 1990s war that erupted as the Soviet Union fell.

But Baku has never hidden its desire to win back control and no state has ever recognised the independence that was self-declared by Nagorno-Karabakh.

The Nagorno-Karabakh separatist authorities accused Azerbaijan of launching an offensive in the south, north and northeast of the region. Baku claimed that Armenians had launched strikes on the Azerbaijani districts of Goranboy, Terter and Agdam.

The fighting, which repeats a pattern seen over the last days, has made a mockery of the ceasefire agreed between the Armenian and Azerbaijani foreign ministers in the early hours of Saturday in Moscow after a marathon session of talks.

Russian Foreign Minister Sergei Lavrov on Monday acknowledged that the ceasefire was not holding and urged both sides to immediately begin implementing it. The European Union and Iran have also called on the parties to properly observe the ceasefire.

But concerns remain over the role of Turkey, which has strongly backed Azerbaijan and stands accused, notably by French President Emmanuel Macron, of dispatching pro-Ankara Syrian militia to assist Baku.

According to the Britain-based Syrian Observatory for Human Rights, 1,450 such fighters have gone to Azerbaijan including 250 who travelled in the last week alone.

It said that 119 of them have died, with 78 of them already repatriated to Syria with other bodies still in Azerbaijan.

Armenia is part of a regional Russia-led security group but Moscow has so far refused to become implicated in the conflict.

Yet analysts say Turkey's involvement will put further strain on the alliance between President Vladimir Putin and Turkish counterpart Recep Tayyip Erdogan.