A new ceasefire agreed to by Armenia and Azerbaijan was again failing to hold on Monday as both sides accused each other of further attacks.
The truce, backed by international mediators, was meant to put a stop to three weeks of fighting over the disputed region of Nagorno-Karabakh.
Hundreds of people have been killed in the fighting already.
The ceasefire was supposed to have come into force at midnight on Sunday but both sides immediately accused each other of breaching the deal.
The Nagorno-Karabakh region is controlled by ethnic Armenians, backed by Yerevan, who declared independence as the Soviet Union fell.
But it has never been recognised by any other state, including Armenia, while Azerbaijan has always made clear its desire to regain control.
On Monday, Azerbaijan's Defence Ministry said Armenian forces shelled areas of four districts in the country overnight.
Meanwhile, the authorities in Karabakh said Azeri artillery fire continued overnight, with the region's army taking "proportionate action" in response.
However, the main city in the enclave, Stepanakert, was quiet overnight, according to an AFP report.
The ceasefire was the second agreed to after a previous truce thrashed out in Moscow this month never showed any sign of seriously holding.
Azeri President Ilham Aliyev accused Armenian forces of "blatantly" breaching the ceasefire, including firing on residential areas, and said people were killed or wounded in the attacks.
He tweeted that Azeri forces had taken control of 13 more Armenian-held settlements.
Azerbaijan repeatedly claimed military success in the fighting by taking control of areas both within Karabakh and in Azerbaijani territory that had been held by Armenian forces.
But analysts say Azerbaijan is unlikely to be able to retake control of Karabakh through military means alone, while the seemingly irreconcilable positions on both sides make a diplomatic solution elusive.
On Sunday, UN Secretary General Antonio Guterres called on Armenia and Azerbaijan to "fully abide" by the new ceasefire, his spokesman said.
The deal was announced after one of the conflict's deadliest attacks on civilians so far on Saturday, when a missile hit a residential area of Ganja, Azerbaijan's second-largest city, killing 13 people, including children.
The clashes over Karabakh erupted on September 27, with more than 700 now dead, according to official tolls, but the real number may be much higher.
