About 20 UN observers have been detained by approximately 30 armed rebels in the Golan Heights on the Syria-Israel border, the international body confirmed Wednesday.

The confirmation came in response to a video posted on the Internet that portrayed men claiming to be Syrian rebels standing next to vehicles marked with the letters "UN".

"The UN observers were on a regular supply mission and were stopped near Observation Post 58, which had sustained damage and was evacuated this past weekend following heavy combat in close proximity, at Al Jamlah," the UN said in a statement.

A man claiming to be from the "Martyrs of Yarmouk" brigade said the convoy would not be released until forces loyal to President Bashar Assad withdrew from the Syrian village of Jamla.

"The command of the Martyrs of Yarmouk announced that it is holding forces of the United Nations Disengagement Observer Force until the withdrawal of forces of the regime of (President) Bashar Assad from the outskirts of the village of Jamla," said the man.

If no withdrawal is made within 24 hours we will treat them as prisoners," he maintained.

The UN said that it is dispatching a mission to assess the situation.

The international body has had its monitors in the area since the 1974 ceasefire between Israel and Syria.