Azerbaijan said on Sunday that Armenian forces had shelled its second city of Ganja in an escalation of the war in the South Caucasus.
Armenia denied that it fired towards Azerbaijan, but the leader of Nagorno-Karabakh, an ethnic Armenian enclave inside Azerbaijan, said his forces had destroyed a military airbase in Ganja.
"Permanent military units located in the large cities of Azerbaijan from now on become the targets of the defence army," Karabakh leader Arayik Harutyunyan said.
Fighting that broke out one week ago between Azeri and ethnic Armenian forces has intensified in the past two days and spread way beyond the breakaway Karabakh region.
It carries the risk of a full-scale war between the former Soviet republics of Azerbaijan and Armenia that could drag in other powers. Azerbaijan is supported by Turkey, while Armenia has a defence pact with Russia.
Local journalists in Ganja said the airport had come under attack.
Ganja, with a population of 335,000, is about 100 km (60 miles) north of the Karabakh capital Stepanakert and 80 km from the Armenian city of Vardenis. Azerbaijan has previously accused Armenia of firing into its territory from Vardenis, and Yerevan has denied it.
Casualties from the past week's fighting have run into the hundreds, although precise figures are impossible to obtain.
Armenia said the Karabakh cities of Stepanakert and Martakert were under attack by Azerbaijan's air force and from long-range missiles.
Each side accused the other of targeting civilians.