Pro-Russian rebel leader Alexander Zakharchenko has refused to engage in peace talks with Kiev.
Zakharchenko said his forces would push the front line back to the borders of Donetsk region, adding that the city of Donetsk was now under their control, the BBC reported.
Refusing to abide by the peace deal signed in September, he said the rebels "will not make any attempts at ceasefire talks any more".
Zakharchenko said that the rebel forces will attack right up to the borders of Donetsk region, but will neutralize it in case of a threat from other directions.
Ukrainian President Petro Poroshenko has accused Russia of deploying more than 9,000 soldiers and 500 tanks, heavy artillery and armoured personnel carriers in eastern Ukraine.
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He urged Moscow to withdraw its troops from the region and meet the terms of a ceasefire plan amid rising tension between Ukrainian troops and rebels in the east, reported the BBC.
Russia has categorically denied the presence of its troops and claims that said it was supporting separatists in the Donetsk and Luhansk regions.
Talks to control the crisis are going on in Berlin. Foreign ministers from Ukraine, Russia, France and Germany are expected to attend the meeting in the German capital.
More than 4,800 people have died and nearly 1.2 million have been displaced after rebels seized control over parts of Luhansk and Donetsk regions in April.
