Sokha, president of the Cambodia National Rescue Party (CNRP), was arrested early Sunday at his home in Phnom Penh after Prime Minister Samdech Techo Hun Sen’s government accused him of conspiring with the United States to overthrow the government.

Sokha’s arrest came a few hours after a video, broadcast by Australia-based Cambodian Broadcasting Network in late 2013, was posted on Facebook on Saturday. The video showed Sokha delivered a speech during a gathering with his supporters in Australia and he told them about his secret plot against the Cambodian government with U.S. support.

“After launching an investigation, examining evidence and listening to the suspect’s answers, the Phnom Penh Municipal Court prosecutor charged Kem Sokha with entering into secret agreement with foreign agents under the article 443 of the country’s Criminal Code and sent him to the Investigating Judge for next legal procedure,” Phnom Penh Municipal Court’s spokesman Ly Sophana told reporters.

The spokesman said the act of conspiracy with foreign agents against the government “is the act of treason.”

Prime Minister Samdech Techo Hun Sen on Monday called on foreign powers to stop interfering in Cambodia’s internal affairs, saying that he would not allow any foreigners to use Cambodians to kill Cambodians anymore.

“We will continue our measures to eliminate the group that destroys the nation, destroy the people’s happiness,” Hun Sen said during the inauguration ceremony of a mosque in southeastern Kampong Cham province.

Sokha, 64, became the president of the CNRP in March 2017, replacing his long-serving predecessor, Sam Rainsy, who resigned in February.

Sam Rainsy, 68, has been living in self-exile in France since November 2015 to avoid at least eight-year-prison sentence for defamation and incitement charges.