Prime Minister Hun Sen has called on foreign countries not to interfere in Cambodia affairs and alleged the United States was helping the opposition Cambodia National Rescue Party (CNRP) to invoke “a regime change” in Cambodia.
Mr Hun Sen also warned that the CNRP could be dissolved if the opposition party tried to defend Mr Sokha.
CNRP President Mr Sokha was arrested in the early hours of Sunday on allegations of treason and was sent to be detained in a prison in Kbong Khmum province, which is about 80 kilometres from Phnom Penh.
He was arrested after video footage from the Australia-based CBN news was posted on Facebook in which Mr Sokha told his audience that the US government had been helping him to change the government in Cambodia since 1993.
Speaking in a meeting with workers on Sunday, Prime Minister Hun Sen said Mr Sokha had betrayed his country and had worked with foreigners to make regime change.
“This issue is very serious,” he said, adding that police would not have made the arrest if it had been a small issue.
He added that Mr Sokha had confessed that the US helped him and used academics and others to plan the change of government.
“We were looking for a third hand and now we found the third hand,” he said.
Mr Hun Sen added that the national elections would proceed as usual. The charge of treason carries a sentence of 15 to 30 years.
The opposition party made no immediate comment on the veracity or content of the video. Earlier, it said Mr Sokha’s arrest was politically motivated and violated the law because of the immunity granted to elected lawmakers.
The party called for his release and urged the international community to intervene. It wanted a non-violent approach, it said.
Neither the US State Department nor the White House responded immediately to a request for comment.
“Freedom of speech is rapidly becoming a highly endangered right in Prime Minister Hun Sen’s march down the road to dictatorship in Cambodia,” said Phil Robertson, Deputy Asia Director of the Human Rights Watch campaign group.
Additional reporting by Reuters