Kiev accused Russia yesterday of sending more tanks and troops into eastern Ukraine and said they were heading towards the rebel-held town of Novoazovsk on the southern coast, expanding their presence on what it fears could be the next battlefront.

Russia did not immediately respond to the accusation which, if confirmed, would go further to kill off a European-brokered truce that was met by relentless rebel advances after it came into force on Sunday. Moscow has always denied accusations that its forces are fighting in Ukraine.

Kiev’s biggest worry is that rebels will continue their advance to threaten Mariupol, a highly strategic port of 500,000 people that is the biggest city still under government control in the two rebellious eastern provinces. Novoazovsk, where Kiev said Russia was reinforcing, lies 40km to the east along the coast near the Russian border.

“In recent days, despite the Minsk ceasefire agreement, military equipment and ammunition have been sighted crossing from Russia into Ukraine,” military spokesman Andriy Lysenko said. He said more than 20 Russian tanks, 10 missile systems and busloads of troops had crossed the frontier.

These are ours now, and we’ll use them against them – we have to expand

The US, which is considering tightening sanctions against Russia and arming Kiev, also says it has sighted Russian reinforcements. The State Department said Russian support for the rebels was undermining international diplomacy and would bring “costs” on Moscow.

Western nations have held out hope they can revive a peace deal brokered by France and Germany in the Belarusian capital Minsk on February 12, even though the rebels ignored it to seize Debaltseve, a town on a strategic railway hub, inflicting one of the worst defeats of the 10-month-old war on Kiev.

In Debaltseve, where Kiev was forced to withdraw thousands of besieged troops this week, the black, blue and red flag of the rebels’ self-proclaimed Donetsk People’s Republic flew over the town hall. Artillery could be heard in the distance. Heavily armed rebels and tanks patrolled the streets on the outskirts, where bridges had been blown up and the railway appeared to have suffered major damage.

A separatist fighter picked out ammunition left by fleeing government troops from the rubble.

“These are ours now, and we’ll use them against them. We have to expand,” said the rebel who refused to give his name.

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