MINSK, Belarus (AP) — Four Ukrainian nationals have been released from separatist captivity and handed over to the Ukrainian government.

The rare prisoner release, originally announced on Thursday, was completed on Friday when the four men were handed over to Ukrainian officials at the airport in the Belarusian capital, Minsk. The men looked tired but had no visible signs of mistreatment or torture. They spent from one to four years in captivity each.

Hostilities between Russia-backed separatists and Ukrainian government troops in eastern Ukraine have killed more than 13,000 people since 2014. Prisoner exchanges between the warring parties became increasingly rare. The last one was arranged in 2017.

Friday's prisoner release was arranged by Viktor Medvedvchuk, a Ukrainian oligarch with strong ties to Russian President Vladimir Putin.