The group said that its employee Christopher Howes, from Bristol, and 28 Cambodians had been seized in Siem Reap province.
A government minister earlier put the number kidnapped from the Svay Chek commune, north-west of the capital Phnom Penh, at up to 24. "We learnt that 12 people had escaped and later on the kidnappers released 10 Cambodians. They are still holding one Cambodian and an Englishman," said the Information Minister, Ieng Mouly, who also heads the Cambodian Mine Action Centre (CMAC). Checks were still being carried out, he added, to confirm whether the kidnappers were Khmer Rouge guerrillas. The Khmer Rouge last kidnapped foreigners in 1994, when at least six captives died.
An MAG spokeswoman said negotiations were under way with the kidnappers, but refused to give details.
MAG said Mr Howes had been working for the group for three years, and was a member of a five-man team of expatriate specialists training civilians in the detection and destruction of anti-personnel mines.