Cambodian police arrested a prominent opposition senator after he angered the country's Prime Minister Hun Sen with a Facebook posting of a disputed document about the border with Vietnam.
Cambodia's strongman leader accused him of "treason" for the posting, and Senator Hong Sok Hour, who belongs to the opposition Sam Rainsy Party (SRP), was arrested on Saturday.
"He was arrested this morning" in the capital Phnom Penh, Ministry of Interior spokesman Khieu Sopheak told Agence France-Presse.
The senator, who is also a French citizen, faces treason charges, Khieu Sopheak added.
Sam Rainsy Party (National Rescue Party) has accused Vietnam of encroaching upon Cambodian territory. In recent months tensions rose between SRP and the ruling Cambodian People's Party even though both parties agreed to a political deal to foster a "new culture of dialogue" last year.
Prime Minister Hun Sen, who has ruled Cambodia for three decades, accused Hong Sok Hour of committing treason for posting a "fake" and "doctored" version of an old treaty about the border, ordering the arrest of the senator who was in hiding.
"The offence is a treason. Please, embassies, don't allow him in if he runs into," he quoted by Reuters as saying.
The opposition often uses the deep anti-Vietnamese sentiment in Cambodia and Hun Sen is sensitive over criticisms of being soft on the issue. Vietnamese troops invaded Cambodia to oust Khmer Rouge regime in 1979 and stayed in the country for a decade. Hun Sen rose to power during the occupation.
Opposition members argue that Hong Sok Hour's arrest was "illegal" because Cambodian senators have immunity from arrest or prosecution. But the government said because he will be charged with treason, he would be stripped of that privilege. The decision is up to the Senate, which is controlled by Hun Sen's ruling party.
Hun Sen has asked UN for permission to borrow the maps drawn by France's Indochina Geographical Service during the colonial period and later lodged with UN in 1964, to compare with current maps used to demarcate his country’s border with Vietnam. Hun Sen’s government has been heavily criticised by National Rescue Party for not pushing claims based on the original map which was prepared by Cambodia and Vietnam’s colonial ruler France over the years of 1933-1953.
Hong Sok Hour joined the border campaign undertaken by the opposition activists in recent years, which included several physical attacks to Vietnamese police and citizens on the border.