Opposition leader Kem Sokha was
Mr Sokha’s arrest and detention was widely condemned by the international community, including the EU, the UN High Commissioner for Human Rights, America and Australia, but China offered its support to the government on the issue.
Court spokesman Ly Sophana said deputy prosecutor Kuoch Kimlong evaluated evidence in the case and questioned Mr Sokha before deciding to charge him with conspiring with a foreign power.
He added that Mr Kimlong had already sent the case to the investigating judge.
Article 443 of the criminal code defines conspiracy with a foreign power as having a secret agreement with a foreign state or its agents with a view to fomenting hostilities or aggression against the Kingdom of Cambodia.
The offence is punishable by 15 to 30 years in jail.
The court released a statement defending the charge, claiming it was legal and followed procedures.
The case against Mr Sokha was based on video footage published by the Australia-based news outlet CBN and other evidence collected by police, the court said.
The statement added that conspiracy with a foreign power was treason as stated in Article 443 of the criminal code, while Mr Sokha’s acts were a “flagrant” crime.
Kem Monovithya, Mr Sokha’s daughter and deputy director-general of public affairs for the CNRP, posted a message from her father in prison on Twitter, saying, “I may lose freedom, but may freedom never die in Cambodia”.
UN human rights chief Zeid Ra’ad Al Hussein said there was international concern over the arrest of Mr Sokha.