SAN BERNARDINO, Calif. - As many as three heavily armed attackers opened fire on a banquet at a social services center for the disabled Wednesday, killing 14 people and seriously wounding more than a dozen "as if they were on a mission," authorities said.

The attackers escaped, setting a large region east of Los Angeles on edge, but about four hours later police riddled a black SUV with gunfire two miles from the late-morning carnage.

A man and woman in the SUV with assault rifles, handguns, and "assault-style clothing" were killed, Police Chief Jarrod Burguan said. A third person who was spotted running away near the scene of the gun battle was detained, but Burguan said it was unclear if that person had anything to do with the crime.

It was the deadliest mass shooting in a nation all too familiar with them since 2012, when a man killed 26 children and adults at a school in Newtown, Conn.

Police shed no light on a motive for Wednesday's massacre, which came just five days after a gunman opened fire at a Planned Parenthood clinic in Colorado, killing three.

In what authorities described as a precision assault, the attackers invaded the Inland Regional Center and began shooting around 11 a.m. local time. They opened fire in a conference area that the San Bernardino County Department of Public Health had rented out for a banquet, said Marybeth Feild, president and CEO of the center.

"They came prepared to do what they did, as if they were on a mission," the police chief said.

Authorities also found a potential explosive device at the social services center.

Burguan said that someone had left the county employees' event after "there was some type of dispute," but investigators were not sure whether that had anything to do with the subsequent massacre.

The Los Angeles Times reported that two law enforcement sources identified one of the deceased suspects as Syed Farook, an American citizen.

Public records show a person named Syed R. Farook was employed by the San Bernardino County Health Department as an environmental health specialist, but it was not clear if that was the same person involved in the shooting.

Hours later, the second slain suspect had still not been identified.

That the violence happened at a place dedicated to helping people with developmental disabilities made it even harder for some to comprehend.

FBI agents and other law enforcement authorities converged on the center and searched room to room for the attackers, but they had apparently escaped. Cervantes, the police spokeswoman, said there were reports from witnesses of one to three attackers.

Several people locked themselves in their offices, desperately waiting to be rescued by police, after the gunfire erupted. Some texted their loved ones or telephoned them and whispered to them what was going on.

Ten of the wounded were hospitalized in critical condition, and three were in serious condition, San Bernardino Fire Chief Tom Hannemann said. Police cautioned that the numbers of dead and wounded were early estimates that could change.

As the search for the suspects went on, stores, office buildings, and at least one school were locked down in the city of 214,000 about 60 miles east of Los Angeles, and roads were blocked off.

Triage units were set up outside the center, and people were seen being wheeled away on stretchers. Others walked quickly from a building with their hands up. They were searched by police before being reunited with loved ones.

One witness, Glenn Willwerth, who runs a business across the street, said he heard 10 to 15 shots and then saw an SUV with blacked-out windows pull away "very calmly, very slowly."

Hours later, with police looking for a dark-colored SUV, an officer in the nearby city of Redlands saw a suspect vehicle and tried to pull it over, a law enforcement official speaking on condition of anonymity said. The SUV crashed, and a gun battle broke out about 3 p.m.

President Obama was briefed on the attack by his homeland security adviser.

He said it was too early to know the shooters' motives, but urged the country to take steps to reduce the frequency of mass shootings. He told CBS that stricter gun laws, including stronger background checks, would make the country safer.

"The one thing we do know is that we have a pattern now of mass shootings in this country that has no parallel anywhere else in the world, and there's some steps we could take, not to eliminate every one of these mass shootings, but to improve the odds that they don't happen as frequently," Obama said.

The shooting sounded like "an organized plot," and preliminary information seems to indicate that "this is personal, and there seems to suggest some element of revenge and retaliation," said Erroll G. Southers, director of Homegrown Violent Extremism Studies at the University of Southern California and a former FBI agent.

The social services center has two large buildings that require a badge to get in, said Sheela Stark, an Inland Regional Center board member. However, the conference room where many public events take place - including the banquet Wednesday - is usually left open when visitors are expected.

This article contains information from the Los Angeles Times.