KIEV, June 20 - President Petro Poroshenko on Friday ordered a seven-day ceasefire in the fight against pro-Russian separatists, but also warned them they could face 'elimination' if they did not use the time to put down their guns.

Poroshenko, installed only three weeks ago as president after seven months of turmoil in the ex-Soviet republic, ordered government forces to cease firing to allow his peace plan for the region to take root.

But after fierce fighting on Thursday about 100 km (60 miles) from the Russian border that apparently caused heavy losses for separatists and some deaths on the Ukrainian side, Poroshenko backed his declaration with a warning to the rebels.

Interfax news agency quoted him as telling military officers in the east that the temporary ceasefire would give the rebels just one week to lay down their arms, after which "they will have to be eliminated."

The ceasefire "does not mean that we will not fight back in the event of aggression towards our military. We will do everything we can to defend the territory of our state," his website quoted him separately as saying.

The ceasefire will run from 10 p.m. on Friday until 10 a.m. on June 27, it said.

After announcement of the ceasefire, Poroshenko launched a 15-point peace plan to end the insurgency in the Russian-speaking east.

In Donetsk, the main industrial hub in the region, the rebels remained unmoved by Poroshenko's ceasefire gesture or the unveiling of a peace plan on Friday.

"What kind of reaction do you expect? When they (the Kiev side) pull out their army, then you will have our reaction," a spokeswoman for the self-styled Donetsk People's Republic said.

Poroshenko's peace plan would offer a safety corridor out to Russia for rebels and volunteer Russian fighters on condition they lay down their arms.

It also calls for establishment of a 10 km (6.25 mile)-wide "buffer zone" along the 1,900 km (1,180 mile)-long border.

The plan would offer freedom from prosecution for separatists who put down their arms and had not committed "serious crimes" and require all hostages to be freed.

It calls for "decentralization" of powers and full Russian-language rights to address the grievances of people in the east.

Ukraine says fighters from Russia and supplies of guns and other military equipment have been pouring into the country to support the separatists.

But though relations with Russia have deteriorated sharply, the pro-Western Poroshenko is under pressure all the same to secure support from Moscow, as well as from his backers in the West, for his plan. On Thursday, he openly appealed to Russian President Vladimir Putin for his support when he outlined the plan in a telephone conversation, his website said.

Poroshenko's new foreign minister will present the blueprint on Monday to his European Union counterparts in Luxembourg. Their support assumes added value after the political association agreement signed between the two sides on June 27. (rt/ez)