KIEV. Ukraine’s President Petro Poroshenko has declared a week-long unilateral ceasefire in fighting with pro-Russian militants in the east of the country.

Heavy fighting had been continuing between Ukrainian government forces and pro-Russia rebels, with new reports of military hardware entering Ukraine.

The ceasefire had been expected ahead of the implementation of a peace plan.

However, correspondents say pro-Russian insurgents seem to have no intention of laying down their arms. 

Poroshenko said the ceasefire "doesn’t mean we won’t fight back against any aggression towards our troops” but that it was intended to give rebels time to disarm.

"We will do everything to protect the territory of our state,” he said. 

Ukrainian news agencies quoted a senior rebel commander as saying the insurgents would not lay their arms until government troops had left the region.

The ceasefire comes a day after Poroshenko held his second phone conversation this week with Russia’s President Vladimir Putin.

The peace plan proposed by Poroshenko promises to decentralise power and hold early local and parliamentary elections.

It also proposes the creation of a 10km (6 mile) buffer zone on the Ukrainian-Russian border, and a safe corridor for pro-Russian separatists to leave the conflict areas.

The White House said it was monitoring what it called a build-up of Russian forces on the border and would "not accept the use of any Russian military forces in eastern Ukraine”.

The latest developments come amid tension between Russia and Ukraine over the removal of pro-Moscow President Viktor Yanukovych and Russia’s annexation of Crimea.

Poroshenko said on Thursday he would sign a controversial association agreement with the EU on 27 June.

Yanukovych was overthrown in February after refusing to sign the deal at the last moment.