A roadside bomb hit a Syrian military truck Wednesday just seconds after the head of the UN observer team drove by, 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 Al-Assad, saying Syria poses an “unusual and extraordinary threat” to US security and diplomatic goals. Wednesday's attack, which wounded eight Syrian soldiers, emphasized the limits of the international plan to use unarmed observers to promote a ceasefire between government troops and rebels trying to topple Assad. The team of 70 UN military observers now in Syria should grow to more than 100 in the coming days. It is unclear when the full team of 300 will arrive. They are to oversee a UN-brokered ceasefire that was intended to allow for talks on a political solution to the conflict but began unraveling shortly after it was due to take effect on April 12. UN 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.” “Such incidents, in addition to the continued violence reported in many cities in Syria, call into question the commitment of the parties to the cessation of violence and may have a direct impact on the future of the (UN) mission,” Ban said in a statement. The bomb went off as Maj. Gen. Robert Mood, the Norwegian head of the UN observer team, drove from the capital, Damascus, to the southern city of Daraa, where Syria's uprising began. The explosion, about 100 meters behind the convoy, shattered the windows of the Syrian military truck and sent up a cloud of smoke and red sand. The truck sped into the city, where several bloodied soldiers were rushed to a hospital. Speaking to reporters later, Mood said it was unclear whom the bomb was targeting. “For me the important thing is really not speculating about who was the target, what was the target, but it is to make the point that this is what the Syrian people (are) seeing every day and it needs to stop,” he said. “Whoever is doing it and whoever is supporting it,” he said. No one claimed responsibility for the bombing.