The U.S. State Department says four people were killed on Tuesday when a bomb blast struck a U.S. Embassy vehicle in Lebanon's capital, Beirut.
Lebanese security officials put the death toll lower, at three. They say the victims were Lebanese and Syrian bystanders.
Speaking in Saudi Arabia's capital, Riyadh, U.S. Secretary of State Condoleezza Rice expressed outrage at the blast. She called it a terrorist act, and she said the United States will not be deterred from its efforts to promote democracy in Lebanon.
The country is currently in a state of political crisis, and it has been without a president since November.
A U.S. State Department spokesman, Sean McCormack says the embassy vehicle's Lebanese driver was slightly injured, and no American diplomats were in the vehicle at the time.
About 16 people were wounded in the blast.
No group has claimed responsibility.