Ukraine and rebels trade prisoners in Donetsk
The rebels were due to swap 150 soldiers for 225 people held by the government.
It appears that most of the captives were exchanged, with the remaining releases due to take place on Saturday.
Meanwhile, Ukraine froze vital bus and rail links with Crimea, its southern territory annexed by Russia in March.
In another move, the world's two largest credit and debit card companies, Visa and Mastercard, said on Friday they could no longer support bank cards being used in Crimea, following fresh US sanctions imposed this month.
The moves come ahead of the traditional holiday season in the region, when people travel to be with their families for New Year.
Inconclusive talks were held this week in Minsk, Belarus, on ending the conflict in eastern Ukraine, which has claimed 4,700 lives.
Although fighting has lessened considerably, the conflict continues and more than 1,300 people have died since a truce was announced in September, the BBC's David Stern reports from Kiev.
Kiev accuses Moscow of actively supporting the militants with Russian soldiers and heavy artillery. The Kremlin denies this but says its regular forces are fighting in eastern Ukraine as volunteers.
Source: BBC