PORTLAND — Federal agents detained at least four people in a sweep of Asian restaurants Wednesday as part of a multi-year, multi-state investigation allegedly involving money laundering, illegal financial activities and the harboring, hiring and transporting of illegal aliens.

United States attorneys filed a complaint in the United State District Court in Portland on Wednesday accusing the “Zhang Operation” — which owns restaurants in Maine, Massachusetts and Rhode Island — of operating “safe houses” where they stored Asian and Hispanic illegal aliens.

The Cumberland County Jail confirmed Wednesday night that federal agents brought in four “immigrants,” but the names, addresses and charges filed against the four individuals were not available, nor would officials say where the four were taken into custody.

The jail said that type of information would have to come from the U.S. Immigration and Customs Enforcement office, which declined to comment through a spokesman. He referred questions to the U.S. Attorney’s office.

Assistant U.S. Attorney Don Clark also declined comment.

Federal immigration agents assisted by police conducted raids at several restaurants Wednesday, including one in Portland.

Westbrook police Capt. Tom Roth said his department provided officers to assist immigration agents with an “operation” in that city, but declined to be more specific.

An employee at Kon Asian Bistro on Brighton Avenue in Portland, one place where vehicles from U.S. Immigration and Customs Enforcement were seen, said the restaurant would be open for dinner Wednesday night and wouldn’t say whether immigration agents had been at the restaurant or made arrests there.

According to media reports, ICE agents were also seen Wednesday at the New China Super Buffet restaurant in Lewiston, at a home in Brewer and at two other restaurants, the Twin Super Buffet in Brewer and the Super China Buffet in Waterville.

According to the complaint, the agency would like to seize 278 Elm Street, a “safe house” in Brewer where the Zhang Operation stored the illegal aliens. The complaint described the house as “squalid” and “deplorable.”

The owner of the house, Ai Hui Lu, is the wife of Zi Zhang. The couple own numerous Chinese restaurants throughout New England, the complaint said.

Since February 2006, ICE and the Department of Homeland Security have investigated the Zhang Operation. The complaint accuses the Zhang Operation of working their illegal aliens as much as 70 hours per week without overtime or benefits.

The operation also did not withhold income taxes from the employees, and it didn’t maintain required employees records. Lastly, it falsified income and business documents, the complaint said.

On Sept. 21, federal immigration agents raided three Mexican restaurants, Fajita Grill in Westbrook and Cancun restaurants in Waterville in Biddeford. Agents arrested eight workers from Mexico and Guatemala, as well as Guillermo Fuentes, owner of Fajita Grill, and his brother Hector Fuentes, owner of the other two restaurants.