Azerbaijan and Armenia clash over disputed Nagorno-Karabakh region

Clashes have begun between Armenian and Azerbaijani forces over the disputed Nagorno-Karabakh region, with at least one Azerbaijani helicopter shot down.
Armenia said Azerbaijan had launched an air and artillery attack. It later declared martial law and total military mobilisation.
Azerbaijan said it was responding to shelling along the whole front. Both sides have reported civilian deaths.
The long-running conflict has flared up again in recent months.