Addis Ababa - A project manager and engineer of Ethiopia's controversial mega-dam who was found dead on Thursday morning was assassinated, police said.

Semegnew Bekele was shot in the head from behind, police chief Zeynu Jemal said. A pistol was discovered inside the car and authorities were trying to establish the owner, Jemal added.

Semegnew's body was found inside a Toyota Land Cruiser parked near a busy road at Meskel Square, Addis Ababa's main public square that is frequented by thousands of people every day.

Prime Minister Abiy Ahmed said he was "saddened and utterly shocked" by the engineer's death.

Semegnew was seen as the main driver behind the 4.8-billion-dollar hydroelectric Grand Renaissance Dam on Ethiopia's border with Sudan. The project caused a long-standing dispute with Egypt, where some fear the dam could reduce the country's share of the Nile waters.