“The investigation has indicated that they must have thought of exploding in two separate places where the spectators were watching,” he said. “From the T-shirts that were found, maybe they were trying to disguise themselves as one of the Ethiopian football fans to get into the halls to explode.”

Ethiopia deployed its military in neighboring Somalia in 2011 to help that country’s government fight al-Shabaab, an al-Qaeda-linked group that’s seeking to establish an Islamic state. Last month, al-Shabaab claimed responsibility for an attack in the Kenyan capital, Nairobi, in which 67 civilians and security forces died. The Islamist militants had threatened to strike Kenya in response to an incursion into southern Somalia by the Kenyan military in 2011.

The blast at a house next to the residence of a U.S. government worker in Addis Ababa’s Bole district occurred 80 minutes before the start of a World Cup-qualifier soccer match between Ethiopia and Nigeria, Redwan said. One of the Somalis rented the property 20 days ago and the other joined him a few hours before the explosion, according to Redwan. Both were in Ethiopia illegally, he said.

Ugandan Attacks

Al-Shabaab carried out coordinated bomb attacks in Uganda in July 2010 that killed 76 people watching the World Cup final. The militia said it targeted Uganda because the country has troops serving in the African Union Mission in Somalia.

The U.S. Embassy in Ethiopia said al-Shabaab claimed responsibility for the Addis Ababa explosion on Twitter and warned of two more bombs in the Churchill Avenue area of the city, which include federal government buildings, and in the city’s Piazza area.

“At this time, we cannot determine the credibility of this threat but, given its gravity, we are sharing it widely,” the Embassy said in a statement posted on its website yesterday.

Three people are being investigated for suspected links to the plot, Redwan said. The government has yet to determine who is behind it, he said.