Authorities launched a manhunt across the Northeast for four Chinese nationals and two Iraqis described by the FBI (search) as potential terror suspects who may be heading for Boston.

Authorities insisted that there was no confirmed threat.

Federal law enforcement officials said they had received a tip Wednesday about an unspecified threat against Boston, and released photographs of the two Chinese men and two women they were seeking. A Transportation Security Administration (search) official said a security briefing indicated the FBI also was looking for two Iraqis.

The governors of Massachusetts and New Hampshire decided to skip President Bush's inauguration Thursday and returned to their states from Washington.

"To assure the people of Boston and Massachusetts that it is safe to be at home, I am going to be sleeping in my bed in Massachusetts tonight and I feel perfectly safe doing so," said Massachusetts Gov. Mitt Romney (search). "In the very remote circumstance that my attention is needed, I will be able to respond on an immediate basis."

The news of the FBI search quickly ballooned into a frenzy of media reports that the suspects planned a radiological "dirty bomb" attack in Boston. But authorities stressed the sketchiness of the information they received.

A federal law enforcement official in Washington, speaking on condition of anonymity because of the ongoing investigation, said the uncorroborated tip was received by the California Highway Patrol. The tipster claimed the men were awaiting a shipment of "nuclear oxide" that would follow them from Mexico to Boston, the source said.

While the term implied some form of nuclear device, such as a "dirty bomb," there is no such material as "nuclear oxide," giving officials yet another reason to question the veracity of the tip, the source said.

Andrew Card, Bush's chief of staff, told reporters Wednesday night that he considered the threat to be based on "sketchy intelligence."

Bruce Cheney, director of New Hampshire Emergency Services, said Massachusetts authorities asked his agency to be ready with radiological testing technicians in case Massachusetts needed them.

"Based on the information we have received from federal officials, it does not appear that there is any cause for alarm," New Hampshire Gov. John Lynch (search) said. "The tip received by the FBI is unconfirmed and uncorroborated."

Massachusetts U.S. Attorney Michael Sullivan and Kenneth Kaiser, special agent in charge of the Boston FBI office, identified the Chinese nationals as Zengrong Lin, Wen Quin Zheng, Xiujin Chen, Guozhi Lin.

Authorities said none of the names had appeared on previous watch lists of terror suspects, and their whereabouts weren't immediately known.

Although federal officials did not give out any information on the two Iraqis, George Nacarra, the Northeast area director for the Transportation Security Administration, said they were mentioned by the FBI during a security briefing Wednesday.

"It was nothing more than they were on the lookout for six people, and two of them were Iraqis," said Nacarra.

Another federal law enforcement official in Washington, also speaking on condition of anonymity, said the FBI's joint terrorism task force has not yet corroborated a tip that the suspects entered the United States through Mexico in recent days, possibly bound for Boston.

Boston Mayor Tom Menino, at a news conference, said there was "a lot of misinformation out there," adding there was no credible basis for those reports.