Hanoi - Vietnam on Thursday confirmed the "urgent arrest" of a Thai and two foreign pro-democracy activists who had been reported missing in the communist country, but refused to say what law the foreigners are accused of breaking.

Government spokesman Le Dung also refused to speak of a fourth missing activist - reportedly a US citizen - who had been arrested while passing out booklets on democracy

"On November 17, the Vietnamese Public Security Agency conducted an urgent arrest and temporary detainment of three people, Nguyen Thi Thanh Van, French passport holder; Truong Leon, US passport holder; and Khunmi Somsak, Thai passport holder; for their violations of Vietnamese law," Dung said at a briefing Thursday.

He said he had no information about the fourth activist, Nguyen Quoc Quan, who the pro-democracy group Viet Tan also claims was arrested over the weekend. Viet Tan identifies Quan as a US citizen.

Dung also refused to discuss what crime the activists are accused of committing.

"Now the people were arrested and detained, and their crimes will be defined later after the investigation," he said.

The detained activists are members of the overseas-Vietnamese group Viet Tan (Reform), which works to end one-party communist rule.

They were arrested while meeting with Vietnamese citizens to discuss "peaceful democratic change" in Vietnam, according to Viet Tan.

Police surrounded the house where the meeting was taking place and then raided the home with more than a dozen officers, seizing materials, Viet Tan said citing a witness to the raid.

Among other things, the activists were passing out copies of a book called From Dictatorship to Democracy in a Vietnamese translation, according to a Viet Tan spokeswoman.

Communist-run Vietnam bans any political opposition and "propaganda against the Socialist Republic" is a crime that carries prison terms of up to 20 years.

In the past year, about a dozen prominent Vietnamese dissidents have been arrested and sentenced to lengthy jail terms, often accused by authorities of colluding with "hostile forces" based overseas.

The French and US embassies in Hanoi said Tuesday they had not been informed by the Vietnamese government of the arrests but were looking into the matter.

Vietnam has in recent years arrested several US citizens working for an end to the Communist Party's monopoly on power. (dpa)