Ukrainian President Petro Poroshenko has vowed to renew operations against pro-Russian rebels, hours after a ceasefire with the separatists in the east of the country expired.

"We will attack and free our lands. The decision not to continue the ceasefire is our answer to terrorists, militants and marauders," he said on his website early on Tuesday. The fragile ceasefire expired on Monday night.

The idea was to give rebels a chance to disarm and to start a broader peace process including an amnesty and new elections. Kiev had accused the rebels of numerous violations of the ceasefire, and a statement tweeted by the Foreign Ministry said 27 Ukrainian servicemen had been killed since the ceasefire began on June 20.

"The unique chance to put the peace plan into practice was not realised," Poroshenko said in a speech prepared for delivery to the nation, the Associated Press reported.

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