The US Embassy restricted the movement of its staff Wednesday and urged Americans to be vigilant a day after a bomb hit one of its vehicles, killing three passersby, in the first attack in more than two decades targeting American diplomats here. US diplomats are deeply involved in the country's fractured politics, supporting the government against the Syrian-backed opposition. The sides have been deadlocked over choosing a new president. The armor-plated Embassy car was damaged in the Tuesday bombing on a north Beirut highway, and its Lebanese driver and an American theology teacher at a nearby church were among 26 people wounded. Two Lebanese and a Syrian bystander were killed.