PHNOM PENH (Reuters) - Cambodia's Senate stripped an opposition senator of immunity from prosecution on Thursday, allowing a court to charge her over comments about Prime Minister Hun Sen amid increasing nervousness over speaking out against the government.

Hun Sen filed a suit against Senator Thak Lany for accusing him in a speech of being behind the July killing of government critic Kem Ley.

A lawyer for Lany, who now faces charges of defamation and incitement, denied the senator had ever made such an allegation.

"Today, we give the rights to the court to bring charges, the immunity was successfully stripped," Senate spokesman Mam Bunneang told reporters, adding that all 46 ruling Cambodian People's Party Senators voted in favor.


Critics have become increasingly worried about speaking their minds about authorities, said Ou Virak of the Future Forum think tank.

"Following the death of Kem Ley, many critics have been afraid to speak out," Virak said.

Hun Sen has ruled with an iron fist for more than 30 years, defeating all challenges to his authority, but he faces a young electorate which appears increasingly hungry for change.

In recent months, tension has been rising between Hun Sen and an opposition hoping to challenge his grip in local elections next year and a general election in 2018.

Several members of the opposition and activists have been jailed as part of what they say is a government crackdown to silence critics ahead of the elections.

On July 10, Kem Ley, a prominent activist and frequent critic of Hun Sen, was murdered in the capital Phnom Penh and Ley's family have fled abroad fearing for their safety.

A suspect has been arrested and police said they believed Kem Ley was killed because of a debt. Activists believe his murder was political.

(Reporting by Prak Chan Thul; Editing by Nick Macfie)