PHNOM PENH - Cambodian police arrested an opposition senator Saturday after the country's strongman leader accused him of "treason" for posting on social media a disputed document about the border with neighbouring Vietnam.
The arrest of Senator Hong Sok Hour, who belongs to the opposition Sam Rainsy Party (SRP), comes amid an uptick in the campaign by the kingdom's main opposition Cambodia National Rescue Party (CNRP) to combat alleged encroachment by Vietnam.
"He was arrested this morning" in the capital Phnom Penh, Ministry of Interior spokesman Khieu Sopheak told AFP, adding that the senator faced treason charges.
Prime Minister Hun Sen, who has ruled Cambodia for three decades, is sensitive to criticism from his opponents that he is too soft on Vietnam over the disputed sections of the two countries' border.
Anti-Vietnamese sentiment runs deep in parts of Cambodia and is often used by the opposition as a touchstone issue to rally support.
On Thursday Hun Sen accused Hong Sok Hour of committing treason for posting a "fake" and "doctored" version of an old treaty about the border on his Facebook page.
It has not been possible to reach the senator for comment or verify the contents of any Facebook post he made.
Senators usually have immunity from prosecution during their terms in office, but Khieu Sopheak said the Hong Sok Hour would be stripped of that privilege because "he committed his offence red-handed".
"His information (posted on Facebook) caused chaos in the country. It is an act of treason," the spokesman added.
Any vote to rescind immunity would have to be taken in the Senate, which Hun Sen's ruling party comfortably controls.
Hong Sok Hour, chairman of the Senate's anti-corruption committee, has played a key role in the CNRP border campaign in recent years. On Thursday the SRP issued a statement denying the senator committed treason.
Rhetorical and sometimes physical attacks by opposition lawmakers and activists on the Vietnamese border have become a common occurrence in recent years.
Last month Hanoi said some 250 Cambodian activists, including a CNRP lawmaker, attacked Vietnamese police and citizens after illegal entering the country, strongly condemning the move.
Vietnam's troops invaded to oust Cambodia's genocidal Khmer Rouge regime in 1979 and stayed in the country for a decade before withdrawing in 1989.
Ties between Hanoi and Phnom Penh have remained friendly under Hun Sen who rose to power during the Vietnamese occupation and has run Cambodia for the last 30 years.
The CNRP formed following a merger between members of the SRP - named after the current CNRP leader Sam Rainsy - and The Human Rights party, ahead of 2013 elections.
The three parties remain in alliance.