Fighting dropped sharply across eastern Ukraine on Sunday but there was still sporadic shooting after a ceasefire came into force, the first step in a fragile peace plan aimed at ending 10 months of conflict.

Fighting dropped sharply across eastern Ukraine on Sunday but there was still sporadic shooting after a ceasefire came into force, the first step in a fragile peace plan aimed at ending 10 months of conflict.

An elderly man and woman died after a Grad missile fire hit the town of Popasna in the Lugansk region some 20 minutes after the truce began at midnight (2200 GMT Saturday), pro-Kiev local governor Gennadiy Moskal said.

The ceasefire in Ukraine was cautiously observed by both Kiev and separatists early Sunday, in line with a deal reached in Minsk earlier this week with the leaders of Russia, Germany and France.

Ukrainian President Petro Poroshenko ordered troops to abide by the truce. However, he said that the peace process was already "threatened" by pro-Russian separatists who have surrounded Ukrainian forces in the battleground town of Debaltseve.

For his part, Donetsk rebel chief Alexander Zakharchenko earlier ordered his fighters to respect the truce but to ward off any attacks "with all force and means".  

Zakharchenko also warned that any attempts by encircled Ukraine troops to escape Debaltseve after the ceasefire will be viewed as an act of aggression.

Earlier on Saturday, Putin was said to have re-affirmed his commitment to the ceasefire in a phone call with Merkel and Hollande.
"Putin said the rebels were ready for the ceasefire," the French presidency said in a statement.

Meanwhile US Secretary of State John Kerry spoke by telephone with Russian Foreign Minister Sergei Lavrov to underscore "the importance of full implementation" of peace agreements, including the ceasefire.

Kerry also "expressed concern about the fierce fighting around Debaltseve, and efforts by Russia and the separatists to cut off the town in advance of the ceasefire," a senior State Department official said.

The UN Security Council is expected to meet on Sunday for an emergency session to shore up the Ukraine peace deal, diplomats said.