An anti-terrorism official in the Cambodian government has filed a complaint accusing former opposition leader Sam Rainsy of “treason” over comments he made in 2013 pledging some “autonomy” to an ethnic minority group.

The lawsuit was filed by Y Sokhy, head of the Ministry of Interior’s Anti-Terrorism Department, late on Wednesday, just hours after Prime Minister Hun Sen ordered a thorough investigation. Sokhy confirmed on Thursday the lawsuit had been filed. The case is pending before the Phnom Penh Municipal Court.

In 2013, Rainsy met with a pro-Montagnard activist in the US, and signed a pledge promising a degree of “autonomy” to the ethnic group, largely quoting the UN Declaration on the Rights of Indigenous People. Hun Sen and other officials claimed Rainsy had promised to cede four provinces to Vietnam, a charge Rainsy denies.

“The counter-terrorism and transnational crime department recommends that the prosecutor of the Phnom Penh Municipal Court take the case on treason and collusion to cut land to foreigners,” the complaint reads, adding that the crime affects “the sovereignty of the Kingdom of Cambodia”.

The lawsuit also claims Rainsy already admitted the charge in a Phnom Penh Post article from March 8. In that article, however, Rainsy denies offering to grant independence or create a separate state, and maintained the word “autonomy” referred to ethnic people’s right to pursue a traditional way of life.

The lawsuit is the latest in a slew of legal attacks on Rainsy, who has lived abroad since 2015 to avoid multiple politically tinged convictions. His successor to the presidency of the opposition Cambodia National Rescue Party, Kem Sokha, was also arrested on widely decried charges of “treason” in September. The CNRP was dissolved at the government’s behest just months before this year’s highly anticipated national elections.

Ly Sophanna, spokesman for the court, confirmed the prosecutor received the complaint.

“The documents are being prepared procedurally,” Sophana said in a message. He did not respond to further questions.

In response to the complaint, Rainsy compared Hun Sen to Pol Pot, saying the infamous Khmer Rouge leader’s “paranoia led him to accuse countless people of ‘treason’”.

“Hun Sen, who served as a military commander under Pol Pot, is following the same path. He is making very expedient accusations to eliminate any opponents to his more and more brutal regime,” Rainsy said in an email.

Additional reporting by Andrew Nachemson