Photographer Serhiy Nikolayev died after artillery fire struck near the village of Pesky, northwest of the rebel-held city of Donetsk, daily newspaper Sevodnya reported in an online statement.

Earlier, Ukraine's military said fighting had eased significantly in the east overnight but reported GRAD missile attacks on the government-held town of Avdiivka, next to Pesky, which is home to one of Europe's largest coke plants.

On Friday, Ukraine reported the first deaths among its servicemen in three days, underscoring the fragility of the truce, as government troops and rebels pulled back heavy weapons from the frontline.

President Petro Poroshenko, who says a military threat from the east would remain even if a peace deal holds, said on Saturday he would submit a bill to parliament to make a formal request for the deployment of United Nations peacekeepers to monitor the ceasefire.

Poroshenko informed U.S. Vice President Joe Biden in a call on Saturday of continued shelling around Donetsk and Mariupol by Russian-backed separatists, the White House said. The two also discussed the inability of the Organization of Security and Cooperation in Europe to verify whether Russian heavy weapons have been pulled back from the front lines, it said.

Biden praised the Ukrainian government's plan to pass reform legislation, recommended by the International Monetary Fund, to stabilize the economy, the White House said in a statement.

The Ukrainian military said the truce had been most fully observed overnight around the rebel-controlled city of Luhansk and near government-held Mariupol on the Sea of Azov.

Kiev fears the port city and industrial hub could become the next rebel target. Rebels humiliated government troops by seizing the strategic town of Debaltseve after the truce was meant to have come into force.

Both government troops and separatists said they continued withdrawing heavy weapons from the front line, "point two" of the peace agreement aimed at ending the conflict, which has killed more than 5,600.