Armenian and Azeri forces have fought new battles, defying hopes of ending nearly three weeks of fighting over Nagorno-Karabakh which US Secretary of State Mike Pompeo says is "a powder keg of a situation".
The worst outbreak of violence in the South Caucasus since Armenia and Azerbaijan went to war over the mountain enclave in the 1990s risks causing a humanitarian disaster and huge economic damage, and could draw in Russia and Turkey.
Pompeo criticised NATO ally Turkey over the conflict, in which Ankara backs Azerbaijan, saying its stance was worsening the situation in Nagorno-Karabakh, which is internationally recognised as part of Azerbaijan but populated and governed by ethnic Armenians.
Turkey has vastly increased military exports to Azerbaijan this year and Russian news agency RIA said the Russian navy had started planned military exercises in the Caspian Sea.
There were further signs on Friday that a ceasefire agreed last Saturday to allow the sides to swap detainees and the bodies of those killed, had all but broken down.
Armenia and Azerbaijan both accused the other of launching attacks and each said it had the upper hand.
Armenian defence ministry official Artsrun Hovhannisyan said Azerbaijan had conducted artillery bombardments in the north of Nagorno-Karabakh, "with total disregard for the humanitarian truce" but added that Azeri forces had been repelled and had suffered significant losses.
"The infantry of the adversary fled from the blows of our army," the ministry added.
Azerbaijan's defence ministry refuted the allegation, saying Nagorno-Karabakh's forces had been forced to retreat and Azeri forces retained the advantage along the line of contact that divides the sides.
The Nagorno-Karabakh defence ministry reported another 29 military casualties, bringing to 633 the number of servicemen killed since fighting broke out on September 27.
Azerbaijan does not disclose military casualties but 47 civilians have been killed and 222 wounded, according to the Azeri prosecutor-general's office.
The hostilities, close to pipelines in Azerbaijan that carry gas and oil to global markets, are stoking concerns in Europe and the US that Turkey and Russia, at loggerheads over Syria and Libya, will be dragged in.
Russia, which brokered last weekend's ceasefire deal, has a defence pact with Armenia.
Pompeo said a diplomatic resolution was needed, rather than "third-party countries coming in to lend their firepower to what is already a powder keg of a situation."
Turkey has rebuffed criticism from NATO allies and accused Armenia of occupying Azeri territory. Armenia accuses Azerbaijan of trying to occupy Nagorno-Karabakh.