Ukraine’s separatist bastion of Donetsk came under intense artillery fire early Sunday, in a level of combat not seen in the region since a barely-observed ceasefire was signed in September.
Firing close to the centre of Donetsk began to build up at 2am, and could still be heard at the same intensity two hours later.
However it was not immediately possible to evaluate the consequences of the artillery bombardment due to an overnight curfew imposed by the rebel authorities in Donetsk and nearby Makiivka.
The Organisation for Security and Cooperation in Europe (OSCE) voiced concern Saturday after its monitors witnessed unmarked columns of tanks and troop carriers moving through east Ukraine in territory held by pro-Russia separatists.
The OSCE report came a day after Ukraine’s military said it had spotted a large column of tanks and other heavy weapons entering the country from Russia across a section of border that has fallen under control of rebel fighters.
Russia denies being involved in the fighting in the east.
However, it openly gives the rebels political and humanitarian backing and it is not clear how the insurgents could themselves have access to so much sophisticated and well maintained weaponry.
Last March, Russian soldiers without identification markings took over the southern Ukrainian region of Crimea, and Moscow annexed the region shortly after.
The OSCE reports from the east came as fears mounted of a total breakdown in the ceasefire signed in September in a bid to end the war, which has killed some 4,000 people, according to UN figures.