A blast that hit troops escorting UN observers in Syria's south on Wednesday was "a graphic example of violence that the Syrian people do not need," said UN observer chief Major General Robert Mood.
The incident in the southern city of Daraa came a day after UN-Arab League envoy Kofi Annan warned that his peace plan could be the last chance to avoid civil war.
"It is imperative that violence in all its forms must stop," Mood was quoted by observer spokesman Neeraj Singh as saying.
Mood, Singh and 11 other observers were in the convoy, but none was hurt.
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"We remain focused on our task," Singh told AFP, adding that the total number of observers in Syria now stands at 70.
Four observers have been deployed to the northern city of Aleppo, Singh added.
Aleppo has witnessed significant unrest in recent days, according to activist accounts.
While the UN monitors' team is expected to grow to 300 in coming weeks, "the number of our military observers today is 70, and will be more than 100 in the next two days," Singh said.
The opposition Syrian National Council accused the regime of being behind the Daraa blast.
"We believe the regime is using these tactics to try to push the observers out amid popular demands to increase their numbers," SNC executive committee member Samir Nashar told AFP.