DOUMA, Syria (Reuters) -- A roadside bomb exploded on Sunday about 150 metres (yards) from a United Nations convoy carrying the head of a Syria ceasefire monitoring mission and a senior UN official in the town of Douma, a Reuters witness said.

Major General Robert Mood's car was stopped at an army checkpoint when the bomb detonated in an nearby alleyway and the convoy left, the Reuters journalist said, adding that there were no reports of casualties.

United Nations Under-Secretary-General for Peacekeeping Operations Hervé Ladsous, who is visiting Syria, was also part of the convoy.

A security source in Douma told Reuters there had been clashes earlier in the day and that gunmen wounded 29 members of the security forces.

Douma, a town on the outskirts of Damascus, is a focus of an armed uprising against the rule of President Bashar Assad which started with peaceful pro-democracy protests in March 2011. The source added that daily life in Douma had come to a standstill due to daily clashes.