Intense artillery fighting has broken out in the separatist bastion of Donetsk in eastern Ukraine, according to AFP journalists in the area.
Firing close to the town centre began at 2:00am (local time) and could still be heard at the same intensity two hours later.
It is the first fighting on this scale since a barely-observed ceasefire was signed in September.
The shelling came after the Organisation for Security and Cooperation In Europe (OSCE) said it was “very concerned” after its monitors witnessed tanks and troop carriers moving through east Ukraine in territory held by pro-Russia separatists.