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 Thursday that the lawsuit had been filed, but declined to comment further. The case is pending before the Phnom Penh Municipal Court.

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

The lawsuit also claims Rainsy already admitted the charge in a Phnom Penh Post article from March 8. In that article however, Rainsy denied ever intending to grant independence or a separate state.

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 party, Kem Sokha, was also arrested on widely dismissed charges of “treason” in September, with their party dissolved shortly thereafter.

Rainsy could not immediately be reached for comment.