Singapore ? Police in Singapore said Thursday they have arrested 13 foreigners, including an American, in an anti-drug operation, less than a week after an Australian was put to death for a narcotics conviction.

Not all of the suspects have been charged. Those who were charged do not face the death penalty if convicted. The defendants include three Britons, an American, seven Thais, a Malaysian and a Japanese. A Singaporean also was arrested.

Nipaporn Ton-sai, 28, of Thailand, faces up to 20 years in prison if convicted of being a drug syndicate leader and trafficker, according to court documents and a statement from Singapore’s Central Narcotics Bureau.

She and her 31-year-old American boyfriend were arrested in the upscale Orchard Road shopping area in a sting operation, officials said.

It was not immediately clear if the American, who was not identified, has been charged. He tested positive for illegal substances, according to the statement.