Cambodian police say they have apprehended a Thai man suspected of gunning down a former opposition politician from Cambodia in a popular Bangkok tourist area.

Thai authorities should immediately and thoroughly investigate the killing of a former Cambodian opposition politician in Bangkok.

A suspected hit man who shot dead a former Cambodian opposition lawmaker in a brazen attack in Thailand's capital Bangkok was arrested in Cambodia after a day-long manhunt, a senior Thai police official said on Wednesday.