Television reports said that Ta Mok, who toppled Pol Pot a year ago and placed him under house arrest, had also been captured. Under Pol Pot's Khmer Rouge regime, as many as 2 million Cambodians died from forced labour, disease and systematic executions between 1975 and 1979.
General Meas Sophea said they had been placed under house arrest in Ba Sa-Ngam, about a kilometre inside Thailand in a mountainous part of the north-east, fairly close to the Khmer Rouge stronghold of Anlong Veng.
The reports come come just one day after the Cambodian government said its troops had captured a key Khmer Rouge rebel base.
Khmer Rouge guerrillas who staged a mutiny nearly three weeks ago against Ta Mok to protest against his allegedly brutal rule were being supported by Cambodian government troops in pursuing him.
Cambodia's King Sihanouk made a low-key return to his homeland after spending three months in China. He was quoted by a Cambodian newspaper as having thrown his support behind a US plan to bring Pol Pot to justice for crimes against humanity. The king's arrival in Siem Reap, near the Angkor ruins, came amid a prolonged battle for control of the Khmer Rouge's Anlong Veng base about 80 miles away.