As the opposition marked the 41st anniversary of the fall of Phnom Penh to the Khmer Rouge, one of its senior officials yesterday lashed out at the imprisonment of a CNRP lawmaker for criticising the government’s handling of the Vietnamese border issue.

Despite his immunity as a lawmaker, Um Sam An, an American and Cambodian dual citizen, was arrested on April 10 and charged on Tuesday.

The political firebrand faces incitement offences for comments posted on Facebook suggesting the government has ceded land to Vietnam by using the wrong map to demarcate the country’s eastern boundary.

Speaking yesterday at an event at the Choeung Ek killing fields to remember the more than 1.5 million Cambodians killed during the Pol Pot regime, which seized Phnom Penh on April 17, 1975, senior opposition figure Kong Korm denounced the government’s actions, saying they undermined the parliament’s integrity and the rule of law.

“Now we don’t even know what the legislative is!” said Korm, who last year retired from his position as a Sam Rainsy Party senator and the party’s president but still advises the SRP, which remains alive at the commune and Senate level despite having merged with the Human Rights Party ahead of the 2013 parliamentary elections.

“[The government] wants to shackle [lawmakers] at any time, and because of this … I resigned. We should work for what? The immunity is meaningless.

“In the Senate, there is no time given to judge or interpret anything; if [the executive branch] says to arrest, then an arrest is made immediately.”

On Tuesday, 63 ruling Cambodian People’s Party lawmakers convened a National Assembly session and voted to allow authorities to pursue the case.

Spokespeople for the CPP were unavailable yesterday. Officials, including the premier, have argued that Sam An’s arrest is legal under a clause of the constitution that allows for individuals to be prosecuted if caught in flagrante delicto, or red-handed, which they say applies because the comments are still online.

Rights groups, however, have disputed the government’s interpretation of the law. CNRP spokesman Yim Sovann said that Tuesday’s vote to approve the case was unconstitutional as the CPP lacked a two-thirds majority, as called for in Article 80 of the constitution.

However, National Assembly spokesman Leng Peng Long yesterday claimed the CPP parliamentarians had acted within their rights.

Yesterday, US Embassy spokesman Courtney Woods said the embassy was “deeply concerned” about the lawmaker’s arrest. “We urge the Cambodian government to apply Cambodian law fairly and without political influence,” Woods said via email.

Meanwhile, CNRP president Sam Rainsy, who is in self-imposed exile to avoid charges also considered politically motivated, yesterday slammed Cambodia’s current leadership, some of whom were Khmer Rouge cadres.

“The Khmer Rouge mentality continues to prevail among Cambodia’s leaders as evidenced by the prevailing culture of violence and impunity, which stems from Pol Pot’s culture of war, elimination and dictatorship,” Rainsy wrote on Facebook.