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"The Minsk protocol envisages the restoration and preservation of Ukrainian sovereignty on all the territory of the Donbass (in eastern Ukraine), including that controlled by the fighters," Poroshenko said.

"There is no question of federalisation or separation of any Ukrainian territory."

The European Union and United States have imposed economic sanctions against Russia over its role in Ukraine, prompting Moscow to retaliate by banning most Western food imports.

The EU has prepared another wave of sanctions targeting Russia's banking and energy sectors but has held off implementing them to see whether the ceasefire holds.

On Wednesday, Poroshenko signed a law allowing Ukraine to impose its own sanctions against Russian firms and individuals deemed to be backing the separatists in eastern Ukraine.

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In Prague, the chairman of the Organisation for Security and Cooperation in Europe (OSCE), which is monitoring the ceasefire, said it would be reasonable to allow more time for the peace process before imposing more sanctions against Russia.

Didier Burkhalter, who is president of Switzerland, also said the OSCE would soon deploy drones to monitor the ceasefire.

Human rights group Amnesty International said in Moscow it had documented evidence of war crimes by both sides and also repeated criticism of Russia's role in the conflict.

"Amnesty International has called the conflict in Ukraine an international conflict and Russia a party to that conflict," the group's secretary general, Salil Shetty, told a news conference.

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Ukraine says Russian forces withdrawing