OSCE lost contact with the four monitors and a translator on May 29 after the group was taken by armed separatists in Luhansk, a stronghold of the pro-Russian resistance.
They were the second team of monitors to be taken in eastern Ukraine. On May 26, a Donetsk-based monitoring group comprised of four people was reportedly detained by a pro-Russian separatist group identifying itself as the Sloviansk self-defense forces. They were released on June 26.
"We welcome the return of the last four of our missing OSCE Special Monitor Mission team mates, after a month away," the OSCE wrote on its Facebook page on Saturday.
Although the OSCE did not detail the circumstances of their release, the Facebook post expressed gratitude that "Many people, both inside and outside the Mission, have worked tirelessly to secure their release, and we take this opportunity to publicly thank them."
The monitors were part of the OSCE Special Monitoring Mission to Ukraine. Despite the abductions in Ukraine's restive eastern region, the OSCE said following the release of the first team that "monitors remain and continue working in Donetsk and Luhansk."
The OSCE added, however, that teams have been reconfigured and the number of monitors in those two regions reduced in light of security concerns.