Pro-Russian rebels in eastern Ukraine have freed four Ukrainian prisoners a day after the two sides exchanged hundreds of captives.
The release was announced by a Ukrainian defence ministry adviser, Vasyliy Budik, who said three were soldiers and the fourth a civilian.
On Friday, rebels freed 146 prisoners for 222 people held by the government, in the biggest such swap to date.
President Petro Poroshenko greeted those freed on Friday at an airport.
Elsewhere, Ukraine has frozen vital bus and rail links with Crimea, its southern peninsula annexed by Russia in March.
Crimea has no land corridor to Russia, and relies on a ferry in the Azov Sea and flights from Russia.
The latest moves come ahead of the traditional holiday season in the region, when people travel to be with their families for New Year.
The releases are part of a 12-point peace plan agreed in September, which also included a ceasefire. Fighting continues, however, and more than 1,300 people have died since the truce was announced.
'More to come'
The latest releases took place without any rebels being freed in return, Mr Budik wrote on his Facebook page (in Russian).
He added that the three soldiers had spent around four months in captivity after being captured at Luhansk airport. The fourth person freed was the head of a factory security guard service, he said.
According to the defence adviser, a further 10-12 Ukrainians could be freed shortly.
Friday's prisoner exchange took place near the town of Avdiyivka, about 35km (22 miles) north of Donetsk.
Ukrainian and Russian media showed rows of men in civilian clothes standing on a road, supervised by armed men.
Among the rebels released by the government are a number of civilians from eastern Ukraine, detained as suspected rebel sympathisers, according to the pro-rebel Donetsk News Agency.
Those released include 35 women, the same source said.
The rebel leadership in Donetsk region has appealed to observers from the Organization for Security and Co-operation in Europe (OSCE) and the Red Cross to investigate allegations of maltreatment by the Ukrainian authorities.
Inconclusive talks were held this week in Minsk, Belarus, on ending the conflict in eastern Ukraine, which has claimed 4,700 lives.
Ukraine accuses Russia 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.
Crimea cut off
People queued at railway stations in Crimea on Saturday to return unused train tickets.
Col Andriy Lysenko, a spokesman for Ukraine's security council, told reporters on Saturday that the freeze on public transport traffic to Crimea was expected to be only a temporary security measure.
The Crimean peninsula - which is also heavily dependent on Ukraine's power supplies - has also seen blackouts in recent days.
Kiev says it has to limit supplies, because Ukraine itself is experiencing power shortages.
The world's two largest credit and debit card companies, Visa and Mastercard, have said they can no longer support bank cards being used in Crimea, following fresh US sanctions imposed this month.
Russian media reported that a number of people in Crimea on Friday were unable to withdraw cash or pay for goods bought in local supermarkets.
Ukraine: The human cost
- 5,200,000 affected by conflict
- 4,707 people killed including 36 children
- 10,322 wounded including 102 children
- 542,080 people displaced inside Ukraine
- 597,956 refugees and asylum seekers outside Ukraine