Debris lies strewn outside the Ethiopian Village restaurant in Kampala, Uganda, on Monday after explosions on Sunday tore through venues where people had gathered to watch the FIFA World Cup final. (Marc Hofer/Associated Press)

An al-Qaeda-linked Somali militant group claimed responsibility Monday for twin bombings in Uganda that killed 74 people watching the FIFA World Cup final on TV.

The group said the militants would carry out attacks "against our enemy" wherever they are.

The blasts came two days after a commander with the Somali group, al-Shabaab, called for militants to attack sites in Uganda and Burundi, two nations that contribute troops to the African Union peacekeeping force in Somalia.

Al-Shabaab, whose ranks are swelled by militant veterans of the conflicts in Afghanistan and Iraq, has long threatened to attack outside Somalia's borders, but the bombings late Sunday are the first time the group has done so.

"We will carry out attacks against our enemy wherever they are," said Sheik Ali Mohamud Rage, a militant spokesman in Mogadishu. "No one will deter us from performing our Islamic duty."

Ugandan officials had said earlier that they suspected the Somali group was involved. One of the targets was an Ethiopian restaurant — a nation despised by the al-Shabaab militants.

The attacks on two venues filled with civilians raised concerns about the capabilities and motives of al-Shabaab, which has been designated a terrorist organization by both Canada and the U.S.

A California-based aid group, meanwhile, said one of its American workers was among the dead. Police said Ethiopian, Indian and Congolese nationals were also among those killed and wounded, police said.

Ugandan government spokesman Fred Opolot said Monday there were indications that two suicide bombers took part in the late Sunday attacks, which left dozens wounded.

Blood and pieces of flesh littered the floor among overturned chairs at the scenes of the blasts, which went off as people watched the game between Spain and the Netherlands.

"We were enjoying ourselves when a very noisy blast took place," said Andrew Oketa, one of the hospitalized survivors. "I fell down and became unconscious. When I regained, I realized that I was in a hospital bed with a deep wound on my head."

Florence Naiga, 32, a mother of three children, said her husband had gone to watch the final at the rugby club.

"He did not come back. I learnt about the bomb blasts in the morning. When I went to police, they told me he was among the dead," she said.

Invisible Children, a San Diego, Calif.-based aid group that helps child soldiers, identified the dead American as one of its workers, Nate Henn, who was killed on the rugby field. Henn, 25, was a native of Wilmington, Del.

President tours blast sites

Ugandan President Yoweri Museveni toured the blast sites Monday and said the terrorists behind the bombings should fight soldiers, not "people who are just enjoying themselves."

"We shall go for them wherever they are coming from," Museveni said. "We will look for them and get them as we always do."

Ugandan army spokesman Felix Kulayigye said it was too early to speculate about any military response to the attacks.

Somalia's president also condemned the blasts and described the attack as "barbaric."

Al-Shabaab, which wants to overthrow Somalia's weak, United Nations-backed government, is known to have links with al-Qaeda.

Ethiopia, which fought two wars with Somalia, is a longtime enemy of al-Shabaab and other Somali militants who accuse their neighbour of meddling in Somali affairs. Ethiopia had troops in Somalia between December 2006 and January 2009 to back Somalia's fragile government against the Islamic insurgency.

In addition to Uganda's troops in Mogadishu, Uganda also hosts Somali soldiers trained in U.S. and European-backed programs.

White House spokesman Tommy Vietor said the U.S. was prepared to provide any necessary assistance to the Ugandan government.

U.S. President Barack Obama was "deeply saddened by the loss of life resulting from these deplorable and cowardly attacks," Vietor said.

Officials said the Sunday attacks will not affect the African Union summit being held in Uganda from July 19-27. Many African leaders are expected to attend.