A former ally of Cambodian Prime Minister Hun Sen was detained by police on Thursday in connection with allegations of illegal drug production from 2012.
Nhek Bun Chhay was taken in for questioning from his home on the outskirts of the capital, Phnom Penh, National Police Deputy Chief Gen. Mok Chito said.
Police did not explain why 5-year-old allegations of involvement in the drug trade had suddenly been revived.
Nhek Bun Chhay was dismissed from his government advisory post by Hun Sen in June following reports that he had conspired with the opposition Cambodia National Rescue Party against Hun Sen's ruling Cambodian People's Party ahead of local elections that month. More than a dozen other members of Nhek Bun Chhay's party also were removed from their government positions.
Hun Sen, known as one of Southeast Asia's wiliest politicians, has used many methods to extend his more than four decades in power, including co-opting and intimidating opponents. In recent years he and his party have been accused of using the courts to pressure their opponents, sending some fleeing abroad and jailing others.
Nhek Bun Chhay formed his own Khmer National United Party last year, which won a single seat in June's local polls, the only one not taken by the two main parties.
Nhek Bun Chhay, then a member of the FUNCINPEC party, led fierce but futile armed resistance against a bloody power grab by Hun Sen in 1997. FUNCINPEC reconciled with Hun Sen and joined a coalition government, and he became a deputy prime minister in 2004.
In 2007, police in Kampong Speu province arrested 18 people and confiscated a lot of drugs and drug-making material. They said one suspect was an adviser to Nhek Bun Chhay, then secretary-general of FUNCINPEC. No legal action was taken against Nhek Bun Chhay at that time.
Police said Thursday that the 2012 allegation applied to activities in Kampong Speu.