Cambodian Prime Minister Hun Sen accused opposition leader Kem Sokha of treason. With elections in 2018, the autocratic ruler is taking few chances as the clampdown goes on.
Kem Sokha was taken away on Sunday morning handcuffed after a raid by between 100 and 200 police, Kem Sokha's daughter, Monovithya Kem, wrote on Twitter.
The police, she said, had arrived without an arrest warrant.
Kem Sokha - who has led the main opposition Cambodia National Rescue Party (CNRP) since his predecessor resigned in February - is expected to be Hun Sen's main challenger in nationwide local elections to be held in June and a general election also next year.
The CNRP said in a statement that the arrest violated the constitution because Kem Sokha has parliamentary immunity. The party called on the government to release its leader.
The government said in a statement on Sunday that it had a video clip and other evidence pointing to "secret plans of a conspiracy between Kem Sokha, others and foreigners to harm the Kingdom of Cambodia," adding that these were treasonable offenses.
Interior Ministry spokesman Gen. Khieu Sopheak said Kem Sokha was detained at the Tropeang Phlong prison facility in Tbuong Khmum province, some 130 kilometers (80 miles) east of Phnom Penh.
He said the next step will be his court appearance to officially face the treason charges, which carry a prison sentence of 15 to 30 years.
"In the video clip that the government obtained, he has admitted himself that he was trained and received funding from a powerful foreign country to topple the government," Khieu Sopheak said. "This is a clear crime and there's no need to make further investigation because he has confessed already."
Fresh News - a pro-government website - said before Kem Sokha's arrest that it had video of Kem Sokha discussing overthrowing Hun Sen with support from the United States.
Clampdown goes on
The arrest represents a further escalation in a campaign against the government's critics, independent media and potential threats to Hun Sen's hold on power before the elections next year.
Hun Sen's government ramped up its attacks on the media, shelving broadcasts by radio stations and ordering an independent newspaper, The Cambodia Daily, to pay a $6 million (5 million euro) tax bill within days. The newspaper said Sunday that as a result of the politically motivated fine it would close down.
Hun Sen, who has been in power for over three decades, has been coming under pressure to maintain economic growth. He only just won the 2013 election against a unified opposition.
The former Khmer Rouge cadre has become one of China's closest regional allies and a vocal critic of the US.
jbh/sms (Reuters, AP)