The assailants who attacked a San Bernardino, CA, office building Wednesday morning killed at least 14 people and left another 14 wounded, the city's police chief said.

They may have opened fire on a holiday party being held by county employees, federal law enforcement sources and a witness told the Los Angeles Times .

The shooting happened on the grounds of the Inland Regional Center, which serves people with developmental disabilities in Riverside and San Bernardino counties.

At a news conference, officials said the motive for the attack remains unclear, and investigators were not sure whether the shooting was an act of terrorism. Sources said the assailants were dressed in camouflage and wearing masks and police think the attackers were carrying long guns, not handguns.

"Is this a terrorist incident? We do not know," said David Bowdich, the assistant director of the FBI's Los Angeles field office.

Keith Nelson, the vice president of the center's board of trustees, said a group he thought to be "county workers" unrelated to the center were hosting a holiday party when the gunfire broke out.

Investigators are now searching for a black sport utility vehicle that may have fled from the Waterman Avenue office building. As many as three suspected shooters fled the building after gunfire erupted, according to the sources. It is unclear whether the people inside the vehicle are witnesses or suspected assailants.