Four Ethiopians were killed in a bomb blast on a bus near the Sudanese border, the information minister said Thursday, as security forces remain on high alert following attack warnings.
"One minibus was blown up on the road and four people were killed," Information Minister Redwan Hussein told AFP, adding it was not known who the attackers were.
The blast occurred Tuesday in Ethiopia's remote Benishangul region, about 400 kilometres (248 miles) northwest of Addis Ababa, bordering Sudan.
The blast followed a government alert warning this week of an increased threat of attacks from Somalia's Al-Qaeda linked Shebab insurgents, who are battling Ethiopian troops based inside Somalia.
However, Tuesday's attack took place far from the Somali border, and in terms of location, it would seem unlikely it was the work of the Shebab.
Last month, two Somalis were killed in Addis Ababa when a bomb they were making exploded. Officials said they planned to target thousands of football fans gathered to watch a World Cup qualifying match.
Redwan warned that Ethiopia still faced threats from neighbouring enemies, including Eritrean-backed insurgents or Somali attackers.
Addis Ababa accuses Eritrea of backing rebel groups inside Ethiopia to destabilise the country, claims Asmara denies.