A prominent activist has gone missing in Laos after his vehicle was stopped by police, his wife said on Wednesday.

CCTV footage revealed that Sombath Somphone, a 62-year-old campaigner for sustainable development, was taken into a police post on Saturday in Vientiane, according to his wife Shui Meng Ng.

He was then driven away in another vehicle with two unidentified people, she said, adding that Mr Sombath's current whereabouts were unknown.

"It is a total shock," she said. "I'm very worried for his safety."

It was unclear why Mr Sombath was apparently detained. Efforts to reach Lao officials were unsuccessful.

Mr Sombath won the 2005 Ramon Magsaysay Award for Community Leadership for his work in poverty reduction and sustainable development in a country that remains one of Southeast Asia's poorest nations.

The United States on Tuesday said diplomatic and aid agency representatives had been in contact with Mr Sombath's wife, adding that it had ``concerns for his well-being and safety''.

``We have registered our concern with the Ministry of Foreign Affairs in Laos and encouraged them to make every effort to locate him and figure out what's happened here,'' State Department spokeswoman Victoria Nuland told journalists.