Tanks, cannons pour into Donetsk, raising fears of more violence
EU calls on Russia to stop further movement of troops, weapons and equipment
Armoured convoys headed to bolster rebel positions in east Ukraine as shelling rocked separatist stronghold Donetsk, prompting US-led concerns of a return to full-scale fighting.
The White House expressed grave concern at reports of Russian military reinforcements in eastern Ukraine, warning that any separatist efforts to seize more territory would be a "blatant violation" of a ceasefire agreement.
"We are very concerned by intensified fighting in eastern Ukraine, as well as numerous reports ... that Russian backed and supplied separatists are moving large convoys of heavy weapons and tanks to the front lines of the conflict," US National Security Council spokeswoman Bernadette Meehan said in a statement on Sunday.
Reflecting the growing unease, the European Union's foreign policy chief, Federica Mogherini, said reports of military reinforcements in Ukraine's separatist areas were a "very worrying development" and called on Russia to prevent further movement of "troops, weapons and equipment".
She also called on all sides to show "restraint" and said Russia should work to find a peaceful solution while respecting Ukraine's sovereignty.
The early hours of Sunday morning in Donetsk saw some of the fiercest combat since the September 5 signing of a frequently-violated ceasefire that halted all-out confrontations across most of the conflict zone, but failed to end constant bombardments at strategic hotspots. Meanwhile the Organisation for Security and Cooperation in Europe voiced concern on Saturday after its monitors witnessed unmarked columns of tanks and troop carriers moving through east Ukraine in territory held by pro-Russia separatists.