Ukranian officials have said that government troops and pro-Russian rebels are withdrawing forces and artillery from frontline positions in eastern Ukraine following in line with a peace agreement.
Monday's withdrawal leaves a 30km buffer between the two sides as part of a nine-point memorandum signed on Saturday.
The agreement came after a truce signed on September 5 was hampered by violations, leading to the deaths of 39 Ukrainian troops and civilians.
However, reduced fire from pro-Russian rebels in recent days has allowed Ukranian forces to begin to pull back troops, said Anriy Lysenko, a Ukranian military spokesman.
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Although the withdrawal has begun, it is "not as large as expected", added Lysenko. "We are seeing a trend that [the rebels] are reducing their use of heavy armed weaponry."
Neither side has completed their withdrawal.
The Ukrainian president, Petro Poroshenko, said that a continued Ukrainian offensive risked alienating support from the US and other Western governments. More than 3,000 people have died in fighting since April.
Separatist regions unresolved
Saturday's agreement does not address the future status of rebel-held regions.
Reporting from Donetsk, Al Jazeera's Robin Forestier-Walker said many rebel-held towns rely on gas that flows from Ukranian government-controlled areas. "That is why [separatists] resent the current cease-fire," he said.
"They want control of the entire Donestsk region."
Ukraine accuses Russia of arming separatists and sending troops into Donetsk and Luhansk in eastern Ukraine, a charge which the Kremlin denies.
On Monday, explosions were heard in the north of Donetsk, where fighting in recent weeks has centred on a government-held aiport.
The Ukrainian president stressed the difficulty of winning the war in rebel-held regions by military power alone.
"The more military groups we have there, the more the Russian army will send," he said.