SAN FRANCISCO — Federal authorities say they have broken up a prostitution ring that had ties to international smuggling operations and used undocumented Asian women as sex workers.

The ring provided sexual services to scores of men each week at four brothels in residential neighborhoods in San Francisco, according to federal court documents unsealed this week.

After working in at least one of the brothels, the prostitutes were sent elsewhere in a smuggling circuit that ran between Canada and U.S. cities such as Los Angeles, Houston, Chicago and New York.

From two to four prostitutes worked at each of the brothels on a typical night, but it was unclear how many women worked for the alleged operation.

On Jan. 14, agents with the U.S. Bureau of Immigration and Customs Enforcement raided four locations in neighborhoods south of Golden Gate Park.

Two days later, they arrested Yuen Ling Poon, a 36-year-old San Francisco woman who authorities say is one of the operation’s leaders. Poon was charged with conspiracy, trafficking of humans for sexual purposes across state and international lines and harboring illegal immigrants. The licensed haircutter was released from custody on $75,000 bail.

Poon and unnamed associates smuggled undocumented women from Thailand, China, Korea and Malaysia to be prostitutes in her brothels. The women, who were typically paid $120 for sex, were ordered to give $40 from each transaction to the brothel operators and kept $80 for themselves, according to affidavits.

Poon’s attorney, Lawrence Wong, said the federal government’s case was flawed because it alleges state, not federal, crimes. The government presents no evidence of smuggling or harboring illegal immigrants, he said.

Bo Song, another woman who allegedly worked at one of the brothels, was arrested for investigation of immigration violations and remains in custody.

Authorities detained several of the illegal immigrant women found working in the alleged brothels.

During the raids, agents seized $31,500 in cash and 3,000 condoms at Poon’s home and confiscated about $120,000 in cash stored in a safe deposit box at a downtown bank.

The investigation started in May when an informant tipped off agents to “the proliferation of underground prostitution houses in the San Francisco Sunset District,” according to the documents.