The country's biggest opposition coalition, the eight-party Medrek, won just a single seat. Medrek and the smaller All Ethiopia Unity Party (AEUP) demanded a rerun, alleging pre-poll intimidation and some vote rigging.

The National Electoral Board (NEB), however, rejected the call, saying neither party had evidence. The Supreme Court on Friday backed the NEB and threw out a case the opposition had mounted, asking that the NEB ruling be overturned.

"The Supreme Court has simply endorsed the decision of the NEB and rejected our appeal against that decision," Medrek chairman Beyene Petros told Reuters.

"There was a total lack of seriousness in reviewing our appeal. Under Ethiopian law, the burden is on the NEB to investigate whatever allegations and evidence we put forward and they didn't do this, which is a violation of the law."

The aftermath of the election is being watched by Western diplomats in a country that is a growing destination for investment and is Washington's key ally in the Horn of Africa, where it is seen as stemming the rise of Islamic militancy.