Phnom Penh: A journalist working for a pro-opposition Cambodian newspaper was killed along with his son in a drive-by shooting in the capital, police said on Saturday.

Khem Sambo, 47, reported on corruption and other social ills under the rule of Prime Minister Hun Sen for the opposition newspaper Moneaseka Khmer.

He was riding a motorcycle with his 21-year-old son on Friday when they were each shot twice by a man who was also riding a motorcycle, Phnom Penh police Chief Yim Simony said. They died later in a hospital.

"At this stage we do not have any leads yet about the motive. We are collecting evidence and witnesses who could help us in searching for the attackers," Yim Simony said.

Moneaseka Khmer editor Dam Sith called the attack "the gravest threat" to his newspaper, which is affiliated with Cambodia's main opposition Sam Rainsy Party. Oum Sarin, president of the Cambodian Association for the Protection of Journalists, said the killing is "creating a climate of fear" among journalists.

The case is the first killing of a Cambodian journalist in five years, according to Pen Samithy, president of Club of Cambodian Journalists.