BANGKOK, Thailand (AP) _ Police arrested 144 Burmese prostitutes who say they were working without pay in prison-like brothels surrounded by barbed wire and guarded by pimps, a welfare group said Friday.

Nearly a third are under 18 years old, according to the Foundation for Children, which is urging police not to press charges and to treat the prostitutes as victims of crime.

The group is affiliated with the Center for the Protection of Children's Rights, a private organization that aided in the raids Wednesday night on three brothels in the southern city of Ranong, 270 miles southwest of Bangkok.

The city is across a small bay from Burmese territory and is a trading and fishing center.

Nine men alleged to be pimps were arrested, including seven Burmese. Newspapers reported that the brothel owners escaped arrest. The brothels were behind the city's immigration office, which is part of the police department.

A number of the women displayed marks on their bodies they claimed were caused by beatings, newspaper reports said. One woman who had become pregnant was quoted in the newspaper accounts as saying she was beaten until she had a miscarriage.

If charged, the prostitutes could face $60 fines or three-week jail terms as well as deportation.

Numerous unconfirmed reports have claimed that Burma's military government punishes repatriated prostitutes. Burmese officials deny the allegations.

The foundation estimates Thailand has as many as 800,000 child prostitutes, while the total number of sex workers may be as high as 2 million.

A small but increasing number of prostitutes are poor young women lured and sometimes abducted from neighboring countries and southern China.

The Thai government began a campaign against child prostitution last year after the murder of a young woman who was seeking refuge after escaping from a brothel in another southern city.

A number of policemen were accused of involvement in the death of the woman, who had her throat slit before being thrown from the window of a city hall building.