She said EU leaders had asked officials to prepare further sanctions in case an agreed ceasefire was not respected.

The leaders of Russia, Ukraine, Germany and France sealed a deal on Thursday after marathon talks in Belarus.

The ceasefire is due to begin in eastern Ukraine at midnight on Saturday but both sides remain sceptical.

Pro-Russian rebels have signed the agreement, which also includes weapon withdrawals and prisoner exchanges, but key issues remain to be settled.

Clashes between government forces and the rebels continued on Thursday and one Russian-backed commander said his forces would not stop fighting.

Thousands of people have died in almost a year of fighting in the region.

In another development, the World Bank said on Thursday it was ready to provide up to $2bn billion (£1.3bn) in financial assistance to Ukraine this year as part of an international package of support.

Tonight, the centre of this rebel heartland is quieter than before. The sound of artillery fire in the distance has become more sporadic but it has not entirely ended.

Donetsk remains a semi-deserted city. Many residents who remember the failure of last September's ceasefire agreement will spend the night in their basements and shelters.

One local told me he hoped the ceasefire would work but said he wanted "New Russia" to remain in the future. "There are only a handful of people who will want to be part of Ukraine," he said.

Rebel forces continue to hold their checkpoints and positions and see no immediate need to retreat. One fighter said he did not trust the other side to stop shooting. Others have told the BBC that they will carry on fighting in the name of their fellow soldiers who have been killed.

'A good morning'

Ukrainian President Petro Poroshenko said implementation of the agreement, reached by leaders in the Belarusian capital Minsk, would be difficult.

A sticking point is the disputed town of Debaltseve, a key government-held town besieged by rebels, where fighting is still going on.

Further talks will also be held on self-rule in parts of Donetsk and Luhansk separatist regions.

(BBC)