Armoured convoys headed to bolster rebel positions in east Ukraine Sunday as shelling rocked separatist stronghold Donetsk and fears mounted of a return to full-scale fighting. Shelling rumbled on throughout the afternoon on the edge of Donetsk, where government forces regularly exchange heavy fire with insurgent fighters, but was less intense than overnight when mortar fire was heard close to the centre for around two hours, an AFP journalist reported. An AFP crew saw a convoy of 20 military vehicles and 14 howitzer cannons without number plates or markings driving through the rebel town of Makiivka in the direction of the nearby frontline around Donetsk. 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.