Azerbaijan's second-largest city, Ganja, has been shelled by Armenian forces, as heavy clashes continue over the disputed Nagorno-Karabakh enclave.
The enclave is officially part of Azerbaijan but run by ethnic Armenians.
The self-proclaimed authorities there said they hit Ganja's military airport after Azerbaijani forces shelled the region's capital, Stepanakert.
Azerbaijan says no Ganja military sites were hit. More than 220 people have died since clashes began a week ago.
Armenia and Azerbaijan went to war over Nagorno-Karabakh in 1988-94, eventually declaring a ceasefire. However, they have never reached a settlement over the dispute.
The current fighting is the worst seen since the ceasefire and the two former Soviet republics have been blaming each other.
There are fears that the actual death toll among the militaries from all sides as well as civilians could be much higher, as casualty claims have not been independently verified.
Azerbaijan's military says its forces have retaken control of seven villages since last Sunday, while Nagorno-Karabakh says its troops have "improved" their frontline positions.
Earlier this week, Armenia said it stood "ready to engage" with mediators from France, Russia and the US to try to agree a ceasefire.
Azerbaijan, which is openly backed by Turkey, has demanded the withdrawal of Armenian troops from Nagorno-Karabakh and adjacent areas seized by ethnic Armenian troops.
"Nagorno-Karabakh is our land," Azerbaijan's President Ilham Aliyev said in a televised address to the nation on Sunday, as he demanded Armenia apologise to his country and provide a timetable for their withdrawal.
"This is the end. We showed them who we are. We are chasing them like dogs."
What's the latest from the battlefield?
In a brief statement on Sunday, Azerbaijan's defence ministry said Armenian forces were shelling Ganja, a western Azerbaijani city lying to the north of Nagorno-Karabakh.
Defence Minister Zakary Hasanov said this was a "clearly provocative" move that was expanding the conflict.
One civilian was killed, local media reported.
In a later statement, the defence ministry said: "The information spread by the Armenian side about the alleged shelling of military facilities in Ganja city is provocative and false.
"As a result of enemy fire, civilians, civilian infrastructure and ancient historical buildings were harmed."
Meanwhile, Nagorno-Karabakh's authorities said that they had destroyed Ganja's military airport.
They said they had acted after Stepanakert was hit by missiles and alleged the Ganja facility had been used by Azerbaijani forces to launch attacks on civilian areas.
Heavy casualties were reported in Stepanakert, which was left without electricity, according to Armenpress news agency. Buses of people were seen leaving the city on Saturday.
Armenpress quoted the separatist region's leader, Arayik Harutyunyan, as warning that "from now on the military facilities permanently deployed in Azerbaijan's major cities are legitimate targets of the defence army".
Mr Harutyunyan added that he had now ordered the shelling stopped, "to prevent the deaths of innocent peaceful civilians".
Turkey condemned the shelling of Ganja, accusing Armenia of "targeting civilians".
But Armenian defence ministry spokeswoman Shushan Stepanyan said that "that no fire of any kind is being opened from the territory of Armenia in Azerbaijan's direction".
Armenia provides military and economic support to Nagorno-Karabakh without officially recognising the self-proclaimed region.
'Casualties all over Ganja'
By Konul Khalilova, Editor, BBC News Azerbaijani
For the more than 330,000 residents of Ganja, this morning brought horror - the city was being shelled by forces fighting for Armenia.
"We heard a big explosion. It was shocking and dreadful. Children were scared," one resident told us. "We left our apartment and went to a shelter."
A nurse in one of the main hospitals said several injured civilians had been brought in.
"My husband saw the body of a woman in a pool of blood. There are casualties all over the city," she said.
Separatists in Nagorno-Karabakh have urged residents of major Azerbaijani cities to leave, warning that military sites there are now legitimate targets.
But Ganja resident Elnur Bayramov said he and his family were not scared.
"We are not going to leave our house, our city, we are not going to become internally displaced people," he said.
Nagorno-Karabakh's authorities have confirmed that 201 of their service personnel and a number of civilians have died since the fighting erupted on 27 September.
Azerbaijan says 22 civilians have been killed, without providing information about its military casualties.
Nagorno-Karabakh - key facts
- A mountainous region of about 4,400 sq km (1,700 sq miles)
- Traditionally inhabited by Christian Armenians and Muslim Turks
- In Soviet times, it became an autonomous region within the republic of Azerbaijan
- Internationally recognised as part of Azerbaijan, but majority of population is ethnic Armenian
- Self-proclaimed authorities are not recognised by any UN member, including Armenia
- An estimated one million people displaced by war in 1988-94, and about 30,000 killed
- Separatist forces captured some extra territory around the enclave in Azerbaijan
- Stalemate has largely prevailed since a 1994 ceasefire
- Turkey openly supports Azerbaijan
- Russia has a military base in Armenia