Both Ukrainian forces and Russian-backed rebels have pulled back most of their heavy artillery from the front line in accordance with a February ceasefire deal, Ukraine’s president said late Monday, amid reports of fresh clashes in the east. However Ukraine's President Petro Poroshenko told a state broadcaster that some heavy weaponry remains in place at the airport in the rebel-held city of Donetsk. World leaders hope the withdrawal of heavy weapons as agreed at high-level peace talks last month will help bring a definitive end to the conflict, which the UN estimates has killed more than 6,000 people and displaced almost 1.8 million. The pullback is being overseen by hundreds of monitors from the Organization for Security and Co-operation in Europe (OSCE), which has in the past cited a lack of cooperation on both sides. Poroshenko said in his interview that exchanges of artillery and rocket fire have largely stopped along the 485-kilometre (300-mile) front.