The F.B.I. is leading an investigation into a fire that was set Wednesday night at the main entrance of the Chinese Consulate General in San Francisco, the authorities said Thursday. No injuries were reported.

The consulate denounced the attack as “despicable” and demanded that the United States move quickly to find those responsible.

An F.B.I. spokesman in San Francisco, Peter Lee, said that the fire had been started by an “incendiary device,” but that it did not appear to have been a bomb. He said the blaze caused significant damage to the building’s doors and charred a large part of the consulate’s exterior before firefighters were able to put it out.

Mr. Lee said the F.B.I., along with the State Department’s Bureau of Diplomatic Security and the San Francisco Police Department, was investigating.