Newaf Khalil, a spokesman for the Kurdish Democratic Union Party (PYD), said the group had been detained by Jaysh al-Islam, a powerful Islamist group allied to Al-Nusra Front, Al-Qaeda's Syrian affiliate.
Khalil said the Kurds were released in exchange for three Islamist fighters who had been detained in Afrin by Kurdish forces. He gave no other details.
"A group of 300 people on five coaches and a mini-bus coming from Afrin were kidnapped at a checkpoint as they went to Aleppo to collect their salaries," Khalil had said after their abduction.
The Britain-based monitoring group also reported that eight people were killed today and 28 others wounded in shelling by the Islamic State group in the central province of Hama.
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The shelling targeted the village of Salamiye, which has a majority Ismaili community, who belong to the Shiite branch of Islam, the Observatory said, adding that the Syrian army retaliated.
Jaysh al-Islam -- one of the numerous armed groups that has surfaced in Syria since the conflict emerged four years ago -- fights alongside Al-Nusra in Idlib but also operates in Eastern Ghouta, near Damascus.
More than 215,000 people have been killed in Syria since the conflict began in March 2011 with anti-regime protests that spiralled into a bloody civil war after a government crackdown.