Russian President Vladimir Putin has called for an end to fighting after clashes broke out in the disputed Caucasus region of Nagorno-Karabakh.
Azerbaijan said 12 of its soldiers and one civilian had been killed and a helicopter shot down. TV images showed a burned out vehicle and craters.
Azerbaijan and Armenia accused each other of starting the fighting.
Nagorno-Karabakh has been in the hands of ethnic Armenian separatists since a war that ended in 1994.
Azerbaijan said its armed forces had come under fire first from large-calibre artillery and grenade-launchers, and that it had taken over two strategic hills and a village.
The Armenian government said Azerbaijan had launched a “massive attack” with tanks, artillery and helicopters.
The Armenian-backed defence ministry in Karabakh said a 12-year-old boy was killed and two other children injured.