Gunmen opened fire on a truck in western Ethiopia Wednesday, killing nine people and injuring seven, the information ministry said.

Gunmen opened fire on a truck in western Ethiopia Wednesday, killing nine people and injuring seven, the information ministry said.

"Unidentified armed men opened fire on a truck carrying 28 people, killing nine on board," it said in a statement.

The motive for the attack was not known, but officials said they were investigating the attack, which took place in the remote Benishangul region, about 400 kilometers (250 miles) northwest of Addis Ababa.

The attack took place near the Grand Ethiopian Renaissance Dam, set to be Africa's largest hydroelectric project.

"Local police and security forces are already deployed to apprehend the perpetrators," the ministry statement said, dubbing the incident a "heinous criminal act".

Ethiopia has witnessed a series of sporadic attacks in recent years, including in March 2012 when 19 people were gunned down on a bus in Gambella in the west of the country.

In January 2012, five foreign tourists were shot dead in northern Ethiopia, an attack government blamed on arch-enemy Eritrea, although a regional rebel group took responsibility lings.

When complete, Ethiopia's Renaissance dam on the Nile River will produce 6,000 megawatts of power.

Egypt has repeatedly voiced concern over the dam's construction, citing fears of depleting water levels on the Nile River and claiming its right to the lion's share of the river's water based on a colonial-era agreement.

Somalia's Al-Qaeda linked Shebab are fighting Ethiopia troops inside Somalia, but have also threatened to attack Ethiopia.

However, the Benishangul region is far from the Somali border, and in terms of location, it would seem unlikely Wednesday's attack was the work of the Shebab.