Armenia has accused Azerbaijan of firing missiles into the capital of the separatist territory of Nagorno-Karabakh while Azerbaijan says several of its towns and its second-largest city have been attacked.
Iran, which borders both countries, said it was working on a peace plan for the decades-old conflict which reignited last month and has killed scores of people on both sides.
The region of Nagorno-Karabakh lies inside Azerbaijan but has been under the control of ethnic Armenian forces backed by Armenia since the end of a separatist war in 1994.
Armenian military officials reported missile strikes in the territorial capital of Stepanakert, which came under intense attacks all weekend.
Residents told the Russian state RIA Novosti news agency that parts of the city were suffering shortages of electricity and gas after the strikes.
Firefights of varying intensity "continue to rage" elsewhere in the conflict zone, Armenian Defence Ministry spokeswoman Shushan Stepanian said on Facebook.