But a party official says the confession was forced and draws comparisons to tactics of the Khmer Rouge.
He says no warrants are needed to arrest them if they return to the country as planned next month.
The three are the latest to face the accusations since the CNRP’s acting chief announced plans to return.
The decision shows there was never any evidence the two reporters committed espionage.
"Millions of people and armed forces are waiting for you on November 9," Hun Sen says in what opposition activists say is a sign he is worried about Sam Rainsy.
At least 30 CNRP activists have been arrested and detained since the beginning of the year.
General Department of Immigration says he expects more expulsions from a larger pool of arrests.
The new charges come a day after authorities accused nine senior CNRP officials of the same crime.
He expects the new migrants will ‘bring insecurity and crime’ to the area in Koh Kong province.
The new charges bolster Prime Minister Hun Sen’s threats to arrest them upon their return.
Sin Bona becomes the most recent opposition victim targeted in a beating by unknown men.
They say that if structures aren't removed, the resort blamed for polluting an area beach will simply be reopened at a later date.
The two men are the latest of nearly 30 opposition activists detained since the beginning of the year.
The two men had voiced support for the return of exiled opposition chief Sam Rainsy.
The Ministry of Justice threatens the public with 15-30 years in prison and life sentences for officials.
The message comes after Cambodia arrests six CNRP activists over the weekend.
Cambodia’s ruling party calls the move ‘propaganda’ and says he will be arrested on arrival.
The new order comes after a court prosecutor charged the acting CNRP chief with ‘insulting the King.’