The FBI (search) on Thursday added the names of nine Chinese people and one other man to the list of those being sought for questioning about a possible terror plot targeting Boston.

FBI spokesman Joe Parris said the names "were developed as a result of the ongoing investigation" but did not signal that credible evidence has emerged indicating such a plot actually exists.

"Information is still uncorroborated and from a source of unknown reliability and motive," Parris said.

The names are part of the same anonymous tip that led authorities on Wednesday to announce that they are seeking to question four other Chinese and two Iraqis. The new names bring to 16 the people being sought for questioning.

Another federal law enforcement official in Washington, speaking on condition of anonymity because of the ongoing investigation, said the tip was received by the California Highway Patrol (search). The tipster claimed the four Chinese — two men and two women — entered the United States from Mexico and were awaiting a shipment of "nuclear oxide" that would follow them to Boston.

The official said the nuclear oxide could be a reference to material used to make a "dirty bomb" that would spew radiation over a wide area.

U.S. Attorney Michael Sullivan (search) of Boston said earlier Thursday that authorities had learned more background about the original four Chinese, but "it makes us no more alarmed this morning, this afternoon, than we were yesterday."

"They're not wanted at this point in time for any crimes because there's no evidence at this point in time that they've committed any crimes," Sullivan said. "We're not certain exactly where they are. We can't even say for certain that they're in the country."

White House Chief of Staff Andrew Card (search) said he discussed the manhunt with President Bush during an Oval Office meeting a few hours before Bush's inauguration for a second term. Card did not provide details on what was said.

The four Chinese previously named by the FBI were identified as Zengrong Lin, Wen Quin Zheng, Xiujin Chen and Guozhi Lin. Authorities said none of the names had appeared on previous watch lists of terror suspects. The bureau also released pictures of those four but not of the others being sought.

One woman was among the nine new Chinese names added: Yu Xian Weng, a woman either 40 or 41 years old. The others were all men: Quinquan or Quiquan Lin, 21; Liqiang Liang, 28; Min Xiu Xie, 27; Xiang or Xing Wei Liu, 22; Mei Xia Dong, 21; Xiuming Chen; Cheng Yin Liu; and Zao Yun Wang.

The final name on the new FBI list was Jose Ernesto Beltran Quinones, of unknown age or national origin.

In Boston, there were visible signs of stepped-up security, including some underground parking garages searching vehicles as they entered and pictures of the Chinese suspects posted inside the booths where subway tokens are sold by transit employees.

It was from Boston's Logan International Airport that two of the planes involved in the Sept. 11 terrorist attacks were launched, and tight security is something residents dealt with in the midst of the Democratic National Convention this past July.

Massachusetts Gov. Mitt Romney, who skipped President Bush's inauguration to return to the state Wednesday night after learning of the threat, sought to reassure residents that there was nothing to be alarmed about.

"These kinds of threats are going to be received from time to time. Generally we're going to be able to deal with them in a prompt manner and dismiss them with time and evidence," Romney said. "It's our hope that this turns out to be an invalid hoax of some kind. ... And yet we take these things very seriously."