SAN FRANCISCO -- A fire set intentionally at the Chinese Consulate in San Francisco is not being investigated as an act of terrorism, U.S. officials say.

The fire was ignited at the front of the building, leading to an arson investigation and calls from the Chinese government for better protection of diplomats in the U.S., the FBI said.

"An incendiary device fueled by gas was detonated at the consulate," David Johnson, FBI special agent in charge of the San Francisco division, said at a news conference Thursday.

Johnson did not provide any specifics about a possible motive or suspects.

No one was hurt in the fire that charred a doorway, damaged the lobby and burned toward the roof. No bomb-making materials were found, the FBI said earlier.

The building was open for business on Thursday with an increased police presence.

Surveillance footage showed a person coming out of a van parked outside with two buckets of gasoline, pouring it on the front of the building and setting it on fire, said Wang Chuan, a spokesman for the consulate.

"We strongly condemn this despicable act and have already made representations with the U.S. on the attack," Wang said. "And we hope that the U.S. takes all necessary measures to provide adequate protection to the consular personnel and properties and bring the culprits to justice as soon as possible."

Firefighters brought the flames under control within minutes, fire department spokeswoman Mindy Talmadge said.

It was not the first time the consulate was attacked. It was struck by blaze in March 2008, when a group poured flammable liquid on a security gate at the rear of the building and set it on fire. No injuries were reported.

That fire came on the day San Francisco supervisors heard public comment on China's human rights record months prior to the 2008 Summer Olympics in Beijing.

The FBI said the 2008 incident was not related to Wednesday's fire.

California Assembly Speaker John Perez condemned the blaze.

"This kind of shameful attack has no place in California," he said.

Associated Press writer Matthew Pennington in Washington, D.C., contributed to this report.