WATERTOWN, Mass. -- Three Pakistani men who authorities say supplied funds to Times Square car bomb suspect Faisal Shahzad were arrested Thursday in a series of raids across the Northeast as the FBI followed the money trail in the failed attack.

Investigators said it was not yet clear whether the three men knew how the money was going to be used.

The men -- two seized in the Boston area, one in Maine -- were arrested as federal authorities searched homes and businesses in a coordinated series of raids centered in the Boston suburbs, on New York's Long Island and in New Jersey.

They were arrested on immigration violations -- administrative, not criminal, charges. They were not charged with any terrorism-related crimes. Their names were not released.

The raids resulted from evidence gathered in the investigation into the Times Square bomb attempt two weeks ago. FBI spokeswoman Gail Marcinkiewicz gave assurances Thursday that there was "no known immediate threat to the public or any active plot against the United States."

In Washington, Attorney General Eric Holder said investigators think there is evidence that the men were providing Shahzad, a Pakistan-born U.S. citizen, with money, but they have yet to determine whether the men knew the funds might have been intended for a terrorist act.

A top Massachusetts law enforcement official, who spoke on condition of anonymity because the investigation is still going on, said investigators are not sure whether the two Boston-area men were willing accomplices or simply moving funds, as is common among people from the Middle East and Central Asia who live in the U.S.

"These people might be completely innocent and not know what they were providing money for," the official cautioned, "but it's clear there's a connection."

U.S. Sen. Susan Collins, R-Maine, said there was "not a direct tie" between the man arrested in South Portland, Maine, and the Times Square car bomb suspect. Authorities have been investigating whether Shahzad was financed from overseas.