Ukraine’s pro-Russian separatists have rejected an offer to lay down their weapons for a week and free hostages so that a definitive peace plan can be thrashed out.

Ukraine’s President Petro Poroshenko says he called a seven day ceasefire in the battle against rebels to give them a chance to surrender.

“It will be a short opportunity for those who fight the legitimate Ukrainian authorities to give up their arms and leave occupied buildings,” he said.

Poroshenko also launched a 15-point plan to end the insurgency in the Russian speaking east which erupted in April after street protests in the capital Kyiv toppled Moscow-backed Viktor Yanukovych.

But Poroshenko’s peace plan has been denounced by the Kremlin which has described it as an “ultimatum”

Speaking at the United Nations in New York, Vitaly Churkin said: “He repeatedly said that the entire world has embraced this initiative but also President Putin and Foreign Minister Lavrov have supported it. I double checked and I’m authorised to say that it is not true. It’s premature to talk about our support.”

Pro-Russian rebels have also remained unmoved by Poroshenko’s ceasefire offer or the unveiling of a peace plan.

It seems the president’s biggest task now will be to win public backing from President Putin despite relations being rock bottom amid Ukrainian accusations that Moscow is fueling the unrest.Charges the Kremlin denies.