The number of foreign sex workers arrested in Malaysia rose sharply last year, in a development which police say is a cause for concern.

"We are concerned about the big increase and trying to find out the reason," said criminal investigations department deputy director Mohamad Mokhtar Hassan.

A total of 6,446 were arrested last year, an increase of 12 percent, he said.

Topping the list were Chinese citizens, who numbered some 2,824 of the foreigners arrested, he said.

Indonesians totalled 1,606, Thais at 910, while the number of Filipinos arrested were 742, he was quoted as saying by the national Bernama news agency.

Other foreign nationals arrested for prostitution included Vietnamese, Uzbeks, Indians and Cambodians.

Economic gain

Mohamad Mokhtar said that around 344 foreign women were rescued from vice activities from 2004 to February this year but added that authorities were finding it difficult to identify true victims of illegal trafficking.

"In certain cases foreign women allowed themselves to be trafficked for economic gain," he said.

"There were cases of women as young as 18 years or below being trafficked for prostitution," he said.

An estimated 142,000 women are currently involved in prostitution in Malaysia, he said.

Malaysian police frequently rescue mainland Chinese women from the clutches of crime syndicates. Many say they were lured to Malaysia with promises of lucrative and legitimate employment.

Prostitution is illegal in the predominantly Muslim nation.