Ukrainian officials say government troops have begun withdrawing heavy artillery in the east of the country, as have pro-Russian rebels in the region.

Col. Andriy Lysenko, spokesman for Ukraine's National Security and Defense Council, said Monday that Kiev's forces had started withdrawing from frontline positions. He said the rebels had also begun their withdrawal of heavy artillery, although it was "not as massive as we expected."

A cease-fire imposed Sept. 5 has been riddled by violations from the start. On Monday, smoke rose over a residential area in the north of the rebel-held city of Donetsk. Lysenko said two Ukrainian servicemen had been killed in the past day.

Last week, an agreement was signed calling for both sides to halt advances and pull back heavy artillery, creating a buffer zone.