DARAA, Syria — A roadside bomb hit a Syrian military truck Wednesday just seconds after the head of the U.N. observer team drove by in a convoy, demonstrating the fragility of the international plan to end the country's bloodshed.
In Washington, meanwhile, President Barack Obama took steps to extend sanctions against the government of President Bashar Assad, saying Syria poses an "unusual and extraordinary threat" to U.S. national security and diplomatic goals.
The attack, which the regime said wounded 10 Syrian soldiers, emphasized the limits of the international community's plan to use unarmed observers to promote a cease-fire between government troops and rebels trying to topple Assad.
The team of 70 U.N. military observers now in Syria should grow to more than 100 in the coming days. They are to oversee a U.N.-brokered cease-fire that was intended to allow for talks on a political solution to the conflict but began unraveling shortly after it was to take effect April 12.
U.N. Secretary-General Ban Ki-Moon condemned the attack, saying the continuing violence undermines the plan, which is "possibly the only remaining chance to stabilize the country and avert a civil war."
The peace plan has been troubled from the start, with government troops shelling opposition areas and rebels attacking military convoys and checkpoints despite the cease-fire.
Many civilians have grown critical of the plan, saying it does not protect them from regime forces.
U.S. State Department spokeswoman Victoria Nuland said the roadside blast that hit troops escorting the U.N. monitors was "further evidence that the cease-fire is not holding."