The CPP jailed Sokha in September on treason charges and banned the CNRP over allegations of a conspiracy to overthrow Hun Sen by force.
Wenguang Sun, who is critical of China's human rights record, has not been heard from since the Wednesday evening show.
The U.S. was joined in its condemnation of the election process by several governments, political figures and rights groups.
The Cambodian government has ordered internet service providers (ISPs) to block the websites of 15 news websites of independent outlets including Voice of America for two days before and during the country’s election.
Reuters could not open the websites of Radio Free Asia Khmer, Voice of America Khmer and Voice of Democracy on Friday.
The criticism came after Rhona Smith questioned the targeting of election boycott campaigners by the Cambodian authorities.
The Center for Strategic and International Studies report found that the Cambodian courts were the main tool used by the authorities to clamp down on civil society groups the authorities saw as challenging.
Communication authorities ordered a 3-month suspension of the Tuoi Tre news website over allegations it ran a report that upset national unity
Hang Puthea, NEC spokesman, said the messages were intended to remind political parties that they must comply with the law, adding that some political parties had already received fines for violations.
In a statement on Wednesday the ministry ordered commune and district officials to issue documents to voters whose identity cards may have been lost or damaged.
Global Witness is launching a campaign that exposes Prime Minister Hun Sen associates who have played a key role in controlling Cambodian politics and its economy in their favor.
Kem Ley's supporters are still calling for an independent inquiry into his murder.