The family of murdered Cambodian government critic Kem Ley has fled abroad, friends of the family said on Wednesday.

Kem Ley, 46, was gunned down in broad daylight at a shop in the capital, Phnom Penh, on July 10. Tens of thousands turned out for his funeral last month, including his heavily pregnant wife, Bou Rachana.

His death comes amid rising political tensions between veteran Prime Minister Hun Sen and an opposition hoping to challenge his grip on power in local elections in 2017 and national elections in 2018.

Bou Rachana, who is seven months pregnant, and her four sons left Cambodia on Sunday in a car, said Buntenh, a Buddhist monk and member of Kem Ley's funeral committee.

"She visited Angkor Wat in Siem Reap for the last time before leaving," Buntenh said, declining to say which country the family fled to.

Buntenh said supporters of Kem Ley had persuaded Bou Rachana to leave Cambodia so she could deliver her baby in a foreign country, and the family will later decide whether to seek political asylum.

Tim Malay, head of local group Cambodia Youth Network, said the family had arrived safely at their destination. "Rachana was worried about her safety and the safety of her family," he said.

Rachana could not be reached for comment on Wednesday.

A 38-year-old-man has been charged with Kem Ley's murder, claiming he killed him over an outstanding debt.

Shortly before he was murdered, Kem Ley gave a radio interview discussing a report by the London-based NGO Global Witness documenting how Hun Sen and his family have amassed millions. The Hun family has dismissed the report.

Many of Kem Ley's supporters say the murder was political and are skeptical of the official reason given for the killing.