Hun Sen berated journalists on Sunday at a dinner his government hosted for correspondents and accused some of spreading fabricated stories.
A Cambodian court on Saturday charged two journalists with espionage for filing news reports to a U.S.-funded radio station.
The US stopped election support for Cambodia with a promise of more "concrete steps" and the EU threatened vital trade preferences banning opposition.
Cambodia's parliament voted to change party laws on Monday to re-distribute seats if a party is dissolved after the government filed a lawsuit.
A royalist political party aligned with Cambodian Prime Minister said it was filing a lawsuit to demand the dissolution of Cambodia's main opposition party.
Cambodian opposition leader Kem Sokha was arrested early on Sunday, his daughter said, and a pro-government website said he had been accused of treason.
Cambodia and Laos reached an agreement for Lao soldiers to pull back from their shared border after Cambodia accused Laos of sending troops into its territory