(CNN) -- Three people from Pakistan were taken into custody Thursday in raids in the Northeast by federal agents in connection with the failed Times Square car bombing, sources close to the investigation said.
Two individuals were taken into custody in Massachusetts, with a third arrested in Maine.
One focus of the probe, according to a source close to the investigation, is a system of "cash couriers" who bring money into the United States from overseas, a method thought to help finance operations like the attempted Times Square attack.
A statement from U.S. Immigration and Customs Enforcement confirmed that three people were taken into custody on alleged immigration violations, but provided no further details.
Two individuals have been under surveillance at least since Wednesday in connection with a cash courier system involving the Times Square bombing attempt, a source close to the investigation said, but the source could not confirm that they were two of the three individuals taken into custody Thursday.
Two of those arrested Thursday are so-called "visa overstays." Another was in the process of being removed from the United States, but had not yet been ordered removed, as he was attempting to adjust his status so that he could stay in the country, the official said.
Attorney General Eric Holder said Thursday that those arrested are tied to Faisal Shahzad, the Pakistani American charged in the May 1 attempted bombing at Times Square, though the exact nature of the relationship is unclear.
"These are people who are connected to Mr. Shahzad -- we're not sure what the connection was," Holder said on a conference call about an unrelated health care initiative. "There is at least a [basis] to believe that one of the things that they did was to provide him with funds, and so we are trying to trace back to see what exactly was the nature of those transactions."
A federal law enforcement source said the initial two people detained were connected to the case, but said they were "collateral" in the sense that they may not have had direct knowledge of or input into the Times Square plot.
Thursday's raids were multi-pronged, following different "tentacles" of the Shahzad investigation, a federal law enforcement source said. "We are focusing on many different things....where and how he got the money, from whom, who he met with, his friends, associates, where he traveled, phone calls, e-mails," the source said.
Investigators were searching locations in and around Boston, Massachusetts, and in New York and New Jersey, a federal law enforcement source said. Agents began executing the search warrants at 6 a.m. Thursday, a federal law enforcement official said.
Two locations on Long Island were among the targets of the raids, a federal law enforcement source said. The FBI executed search warrants at both locations in Suffolk County, New York, in eastern Long Island, the source said. Tim Motz, a Suffolk County Police spokesman, said officers from that department were assisting federal agents. No arrests had been made.
Some of the money allegedly ferried by the cash couriers is thought to have been made available to finance operations like the abortive Times Square attack. The source close to the investigation said two individuals have been under surveillance at least since Wednesday, but could not confirm that they were two of the three individuals arrested in the raids.
The source said there is no direct evidence connecting those under surveillance to the Times Square attempted bombing, but they are being investigated for possible links.
"These searches are the product of evidence that has been gathered in the investigation since the attempted Times Square bombing and do not relate to any known immediate threat to the public or active plot against the United States," Attorney General Eric Holder told the House Judiciary Committee on Thursday. "I share that information just to indicate that this is an ongoing investigation and that we are actively pursuing all those who were involved in it."
One of the searches took place in Watertown, Massachusetts, according to a federal law enforcement official. CNN affiliate WCVB-TV reported that two people were taken into custody in Watertown.
A Watertown resident who lives near the home where the search warrant was executed told WCVB he was sitting in his living room watching television at about 6 a.m. when he "heard an FBI agent scream, saying 'Don't move' or 'Put your hands up,' something like that."
"I thought I was dreaming, actually, because in a small town, who would think, you know, that you'd hear an FBI person?" said the man, who did not give his name in the interview posted on WCVB's website.
When he looked out the window, he said, he saw 15 or 20 FBI agents lined up, with their guns drawn and pointing at the house. He said after a few minutes, a couple of agents went inside the house. "I was expecting to hear gunshots or something, you know, but there wasn't ever any gunshots," he said.
After a few minutes, agents brought a man out in shackles, put him in a car and drove away, the man said. He said he'd never seen the man before, but noted that new residents have moved into the home every few years.
Photos from Watertown showed yellow police crime scene tape around a large white Colonial-style house. The photos were taken by WickedLocal.com, a local news website.
One photo showed a man in an FBI shirt talking with two other men. Another showed a man walking out of the house holding a plastic bag that appeared to contain an electronic or computer-related device or accessory.
Another search unfolded in Brookline, Massachusetts, where police were helping the FBI search a Mobil gas station on Harvard Street, said Lt. Philip Harrington of the Brookline Police Department.
Video from CNN affiliate WHDH-TV of Boston showed apparent law enforcement officers at the gas station. They were examining a parked gray four-door sedan, its two front doors and trunk open.
Diane Chung, who manages a Japanese fusion restaurant across from the gas station, said investigators were swarming the scene when she got to the restaurant around 9:30 a.m. She said the gas station was completely blocked off.
She said she hadn't seen authorities bringing anyone out of the gas station and hasn't seen them enter any other businesses in the area.
Michael Sobelman, owner of Michael's Deli on Harvard Street, took a stroll down the street to check out what he said was rare commotion along the retail and commercial stretch.
"You can see them taking stuff out," he said. "You'd never have thunk something like this is going on."
News media and police packed the area as three or four helicopters hovered over the scene. Sobelman said he saw the FBI load vehicles with material from the gas station.
"I'm shocked that it could happen in an affluent community like this," Sobelman said. "I tip my hat to the FBI and praise them for their work and their diligence and looking behind the scenes into everything."
A search warrant was also being executed at a home in Cherry Hill, New Jersey, according to J.J. Klaver, FBI spokesman in Philadelphia, Pennsylvania. No one was in custody. A federal law enforcement source told CNN raids were also being conducted at a business called Prompt Printing in Camden, New Jersey. The home in Cherry Hill was believed to be that of the shop's owner, the source said.
Shahzad, a 30-year-old Pakistani American, is the only person charged in the May 1 attempted bombing at Times Square.
He was arrested while trying to fly out of New York two days after he allegedly attempted to set off a car bomb in the always-crowded tourist hotspot. The bomb failed to detonate.
President Barack Obama appeared at New York Police Department headquarters Thursday to thank law enforcement for their efforts to combat terrorism. "What we saw in Times Square is that you know how to get the community involved in raising awareness, which is absolutely critical," Obama told the officers, alluding to the T-shirt vendor who alerted police to the suspicious vehicle involved in the New York plot. "And as a consequence you have saved an awful lot of lives."
Shahzad has been charged with five counts in connection with the case.
According to court documents, he admitted to law enforcement officials that he attempted to detonate the bomb and that he recently received bomb-making training in the Waziristan region of Pakistan.
Court documents also said that Shahzad returned to the United States via a one-way ticket from Pakistan on February 3. He had told immigration officials upon his return that he had been visiting his parents in Pakistan for the previous five months, the complaint said.
Holder said Shahzad was working with the Pakistani Taliban.
Sen. Dianne Feinstein, D-California, urged Secretary of State Hillary Clinton in a letter Thursday to add the Pakistani Taliban to the State Department's list of foreign terrorist organizations. Feinstein chairs the Senate Intelligence Committee.
CNN's Susan Candiotti, Cassie Spodak, Kathleen Johnston, Jeanne Meserve and Joe Sterling contributed to this report.