DONETSK: Heavy artillery fire on Wednesday rocked east Ukraine’s pro-Russian rebel bastion of Donetsk, after international monitors warned over escalating violence following the arrival of columns of insurgent reinforcements.

The explosions of mortars being fired from near the center toward government positions at the ruined airport rumbled on from early in the morning, setting off car alarms, an AFP correspondent said.

Donetsk’s city hall said in a statement “the sound of artillery fire and explosions can be heard in all districts” of the mining hub.

Ukraine’s military said Wednesday one soldier had been killed and two wounded, including one at the airport, as its positions came under repeated shelling around the region.

The intensified shelling, the heaviest since the weekend, comes after observers from the Organization for Security and Cooperation in Europe (OSCE) in east Ukraine warned that growing clashes could tip the region back into all-out conflict despite a cease-fire deal.

A frequently-violated truce has been in place in the east of the former Soviet republic since September.