The exchange took place at a checkpoint in the vicinity of a bridge across the Kazyonny Torets River in Slavyansk, the Slavgorod newspaper said.
It named the Alfa servicemen as Maj. Serhiy Potemsky, Capt. Yevhen Varynsky, and Lt. Col. Rostyslav Kiyashko.
Self-defense spokeswoman Stella Khorosheva said Gubarev was currently traveling to Donetsk.
Vyacheslav Ponomaryov, people’s mayor of Slavyansk, said three Ukrainian Security Service officers have been exchanged for self-defense activists, including the Donetsk region’s people’s governor Pavel Gubarev.
“Pavel has indeed been released. We have exchanged three Ukrainian Security Service officers for three of our activists, including Pavel,” he told Interfax by phone.
Ponomaryov said Gubarev is now on the territory controlled by the Donetsk region’s self-defense forces.
Pavel Gubarev, commander of the Donetsk region’s self-defense forces, was declared the new governor of the Donetsk region at a rally held by anti-maidan activists in Donetsk on March 1.
Gubarev and his supporters earlier made several demands to the local authorities, including to hold a referendum on the status of the region.
Gubarev was detained in Donetsk on March 6.
Protesters in Donetsk demanded that the release of the people’s governor in March-April.