A Cambodian political analyst was jailed for 18 months on Thursday for accusing prime minister Hun Sen's ruling party of having a hand in the murder of prominent government critic.

Kem Ley was gunned down in July last year while drinking coffee outside a petrol station in the capital in a brazen daylight murder that sent a tremor through civil society groups.

A former soldier, who calls himself "Meet to Kill", was sentenced to life imprisonment in March for the killing.

Political analyst Kim Sok was charged with defamation and inciting unrest for comments in a radio interview suggesting links between the ruling Cambodia People's Party and the shooting.

The complaint was brought by Cambodia's strongman premier Hun Sen who has ruled the country for over three decades.

A Phnom Penh court on Thursday found Kim Sok guilty of the charges and sentenced him to 18 months in prison, ordering him to pay $200,000 in compensation to the ruling party.

Kim Sok's comments could have ignited anger among the public "that would lead to chaos in the society",  Judge Ky Rithy said.

A defiant Kim Sok refused to stand up before the judge, prompting four prison guards to force him to his feet.

He also demanded a re-trial, yelling "I don't respect a scarecrow judge."

Hun Sen is renowned for using Cambodia's pliant courts to tie-up his critics -- including activists and the opposition party, which is hoping to oust him in elections next year.

Some 27 political prisoners have been thrown in jail since 2013 with dozens of ongoing prosecutions against others, according to a tally by Amnesty International. 

Hun Sen, one of the world's longest serving leaders, portrays himself as a premier who has brought growth and stability to an impoverished country ravaged by decades of war.

But many Cambodians, especially the young and city-dwellers, say corruption, inequality and rights abuses have flourished under his watch, raising the prospect of a tight general election next year.