Ukrainian government forces and Russian-backed separatists have started withdrawing small-caliber weapons from the front line.
Military spokesman Ruslan Tkachuk said the "synchronized withdrawal from the front line" began on October 5 in the eastern Luhansk region, involving tanks, antitank cannons, and mortars.
The rebels in Luhansk confirmed that the weapons were being withdrawn.
Later, the separatist forces in the Donetsk region are also scheduled to withdraw weapons from the front line.
Arms with a caliber of less than 100 millimeters are to be pulled back a distance of 15 kilometers within 41 days.
A spokesman for international monitors in the area, Michael Bociurkiw of the OSCE, told the BBC there was "encouraging" movement of heavy weapons.
The pullback is part of the cease-fire agreement signed in Minsk in February.
The conflict in eastern Ukraine between separatists and government forces has left more than 7,900 dead since April 2014.