BEIRUT (Reuters) - Al Qaeda's Syrian offshoot, the Nusra Front, said it had executed around a dozen pro-Syrian government captives on Wednesday in retaliation for a government advance near Damascus.

A video distributed by the group showed at least 12 men who gave their names before kneeling down in a line and being shot simultaneously in the back of the head.

Nusra Front said in a statement the executions were a punishment for a government advance into Harira village in the Wadi Barada area northwest of the Syrian capital Damascus and near the Lebanese border.

Wadi Barada is a mountainous valley held by rebels, but the Syrian government controls much of the surrounding territory. It contains a water spring which supplies much of Damascus.

The Syrian Observatory for Human Rights said air strikes and pro-Syrian government ground troops attacked Harira and other areas in the Wadi Barada area on Wednesday.

The Observatory said it had seen a video purporting to show a group of soldiers captured by Nusra a few days ago. One of the captive soldiers said there were 14 captives and pleaded in the video for Syrian government forces not to enter Harira and another village nearby because if they did, Nusra Front would kill the detainees.

(Reporting by Lisa Barrington; Editing by Hugh Lawson)