PHNOM PENH (Reuters) - Cambodia’s security forces are “actively campaigning” for the ruling party of Prime Minister Hun Sen ahead of a general election on July 29, in violation of a law requiring political neutrality, Human Rights Watch said on Thursday.

A supporter of the ruling Cambodian People's Party (CPP) uses a mobile phone to photograph a portrait of CPP president Hun Sen during an election campaign in Phnom Penh, Cambodia, July 7, 2018. REUTERS/Samrang Pring

Hun Sen, who has ruled Cambodia for 33 years, wants to ensure victory after two close elections in 2013 and 2017 with a crackdown on his critics, spurring many rights groups and the main opposition to call the vote a sham.

He is widely expected to win the election after the Supreme Court dissolved the main opposition Cambodia National Rescue Party (CNRP) last year, leaving no significant competitor for Hun Sen’s Cambodian People’s Party (CPP).

“Basic democratic principles require the political neutrality of the military and police for elections to be free, fair, and credible,” said Brad Adam, Asia director of the New York-based group.

“Nothing about this election is democratic, so it is hardly a surprise that the CPP is using senior commanders as ruling party campaigners,” Adams added in a statement.

Sok Eysan, a spokesman for the CPP, dismissed HRW’s concerns, saying members of the security forces could campaign legally, so long as they limited participation to their days off, did not carry weapons or wear official uniforms.

“Brad Adam has had anger and grudge against the CPP for a long time,” Sok Eysan said.

Last weekend, Hun Sen launched a three-week election campaign with rallies across the capital Phnom Penh, as did other, smaller parties.

But there was no sign of the main opposition CNRP, many of whose leaders have fled Cambodia over the past year fearing a crackdown by Hun Sen and his allies.

CNRP leader Kem Sokha was arrested in September for alleged treason, an accusation he denied. The CNRP was dissolved by the Supreme Court in November at the government’s request.