One of the 13 Chinese nationals allegedly involved in a terror plot against Boston was in custody and being questioned by authorities on Saturday, FBI sources told FOX News.

Authorities were interrogating Mei Xia Dong about her involvement in a possible terrorist plot (search) against Boston that was made public in an FBI report Friday. Airport and transit authorities responded to the report by boosting security — adding patrols, activating radiation detectors and posting pictures of some of the suspects.

FBI agents were looking into an uncorroborated tip that 16 people — 13 Chinese nationals, two Iraqis and one other person whose nationality was not released — might be planning an attack.

The agency announced Wednesday that it was investigating four Chinese nationals, and a Transportation Security Administration (search) official said later that a security briefing indicated the FBI also was looking for two Iraqis. The number jumped by 10 Thursday "as a result of the ongoing investigation" but did not signal that credible evidence about a plot had emerged, FBI spokesman Joe Parris said.

The 14th person was identified on the FBI's Web site as Jose Ernesto Beltran Quinones, but his nationality was not given.

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

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.

Several radioactive compounds take form as oxides and could be used in a dirty bomb, expert Charles Ferguson said. Plutonium and americium oxides, in the right amounts, would be dangerous to human health, while uranium oxide would be less so, he said.

"They vary in potency," said Ferguson, science and technology fellow at the Council on Foreign Relations in Washington. "If it was plutonium, we could have a problem on our hands."

At Logan Airport, where two of the planes were hijacked for the Sept. 11 terrorist attacks, the tip was being taken seriously, according to Dennis Treece, director of corporate security. The most visible sign was more patrols.

The Massachusetts Bay Transportation Authority, the city's transit agency, also increased security and activated radiation detectors in response to the threat, said Deputy Chief John Martrino. He said the detectors are put in use whenever the city is on higher-than-normal security alert.

Pictures of four Chinese suspects released by the FBI were taped inside booths where subway tokens are sold by transit employees, and operators of underground parking garages started searching vehicles. Dong, the suspect in custody, was not one of the four in the pictures released by the FBI.

Barbara Fisher of suburban Belmont, waiting for the subway at Boston's South Station, said she wondered if she should plan another way to get to her vocational training classes if the subway shut down. But she said she was reassured when authorities said the threat was uncorroborated.

"You can't be too nervous," she said. "I'm not changing my life."

Patrice Diaz-Migoyo, a graduate student at the Massachusetts Institute of Technology, said he believes it's hard to assess threats because of past government intelligence failures and secrecy.

"Do I personally feel threatened? No," he said, standing inside an upscale downtown shopping mall where security is usually tight. "Should I? I have no means to judge."

But he said the news reports brought back memories of the 2001 attacks on New York and Washington.

"My first reaction, because I lived in Greenwich Village on Sept. 11, was annoyance if I happened to be in the two cities that got struck," he said.

The Rev. John R. Odams, pastor of Pilgrim Church, United Church of Christ, in Boston's Dorchester section, said he wasn't worried.

"Emotional terrorism is probably a greater threat to us," he said as he waited for a train. "We need to look at the bigger picture.

"It seems there are so many other dangers in our society that end up getting ignored — housing, homelessness, poverty — that are in some ways more threatening," Odams said.