Ethiopia Ambush
Labourers work at the Grand Renaissance dam near the scene of the bus attack which claimed nine lives   Reuters

Unidentified gunmen have ambushed a bus in western Ethiopia killing nine and leaving six wounded, according to government officials.

Government spokesman Redwan Hussein said the ambush occurred in the Banishangul Gumuz region, in close proximity to the country's $4 million Grand Renaissance Dam and the Sudanese border.

"The bus was targeted while travelling 100 kilometers (62 miles) south of (regional capital) Assosa," a state-owned Ethiopian Television report said.

The bus was transporting 28 people when the gunmen struck in the region which has a heightened security presence because of the dam's construction.

No group has yet claimed responsibility for the attack but Ethiopian authorities have previously foiled attacks by al-Shabaab Islamist militants and Ethiopian insurgents.

The gun attack is the second on public transport in the Benishangul Gumuz region in the space of five months after four people died in a minibus bomb blast in November 2013.

Hussein told Associated Press that no arrests had been made but authorities were pursuing suspects.