Seven police detectives in Pathum Thani have been transferred to inactive posts pending an investigation into the alleged rape and extortion of a woman drug suspect.

Pol Lt Gen Jirasan Kaewsaeng-ek, commissioner of Provincial Police Region 1, provided details on Tuesday.

The complainant said she was detained on Nov 22-23. An initial inquiry showed a drug arrest during that period, but there was no immediate evidence of extortion or rape, he said.

"If the investigation finds that they did wrong, they will face both disciplinary action and criminal action. Any police involvement in extortion and rape is intolerable," Pol Lt Gen Jirasan said.

The woman who made the charge works in public relations. Her name was not released.

At the government complaints centre near Government House on Tuesday, she and her boyfriend, their faces covered, said that detectives searched them at a restaurant in Rangsit area of Pathum Thani and found ketamine and methamphetamine pills.

Their mobile banking app revealed the couple had 360,000 baht in account deposits. The officers allegedly demanded 300,000 baht in exchange for reducing the charge against them to possessing two methamphetamine pills, instead of a ketamine possession charge and assets seizure.

They were taken to ATMs in Pathum Thani and made to withdraw a total of 300,000 baht in cash, the couple alleged.

One detective then took the woman to a motel in Pathum Thani, where she was allegedly raped. The woman said she was forced to have sex and to hand over another 30,000 baht in cash, in exchange for "a successful negotiation with a superior to limit the charges".

Her boyfriend learned about the sexual assault only after being released on bail. He had been held at Thanyaburi police station for possession of two methamphetamine pills.