Armenia and Azerbaijan accuse each other of violating a humanitarian ceasefire agreed three days ago to quell fighting over Nagorno-Karabakh, drawing warnings from international groups of a humanitarian crisis in the region.
A Reuters cameraman on Tuesday witnessed shelling in the town of Martuni in Nagorno-Karabakh, a mountain enclave which is internationally recognised as part of Azerbaijan but governed and populated by ethnic Armenians.
A Reuters television crew in Terter in Azerbaijan also said the city centre was being shelled earlier on Tuesday.
The Russian-brokered ceasefire, aimed at allowing the sides to swap prisoners and bodies of those killed, is buckling, dimming peace prospects after deadly clashes broke out on September 27.
Azerbaijan's defence ministry said Armenian forces were shelling the Azeri territories of Goranboy and Aghdam, as well as Terter, and "grossly violating the humanitarian truce".
"Azeri armed forces are not violating the humanitarian ceasefire," defence ministry spokesman Vagif Dargiahly said.
Armenian defence ministry spokeswoman Shushan Stepanyan denied the accusation. She said Azeri forces had resumed military operations after an overnight lull.
The flare-up of fighting is the worst since a 1991-94 war over Nagorno-Karabakh that killed about 30,000.
It is being closely watched abroad partly because it is close to Azeri gas and oil pipelines to Europe, and Turkey and Russia risk being dragged in. Russia has a defence pact with Armenia, while Turkey is allied with Azerbaijan.
Turkey is not involved in the mediation, which has been led by France, Russia and the United States. Ankara says it backs Azerbaijan's offensive to "retake its occupied lands".
The death toll has continued to rise. Ethnic Armenian officials in Nagorno-Karabakh said their military death toll was 542, up 17 from Monday.
Azerbaijan has reported 42 Azeri civilian deaths and 206 wounded since September 27. It has not disclosed military casualties.
Martin Schuepp, Eurasia regional director for the International Committee of the Red Cross, said his organisation was in "continuous discussions" to facilitate the handover of detainees or bodies of those killed but no meaningful agreement had been reached.
"The security situation has also been such for us and our teams that it has not been possible for us to access all locations that might have been affected," Schuepp said.
The conflict was also worsening the spread of COVID-19 across both countries, Tarik Jasarevic told a United Nations briefing in Geneva.
Australian Associated Press