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A Somali terrorist group tied to Al Qaeda reveled in the tears and blood they spilled in Uganda as they claimed responsibility for simultaneous bombings that tore through World Cup parties in the country's capital Monday night, killing 74 people.

Al-Shabab militants said they would carry out attacks "against out enemy" wherever they are. "No one will deter us from performing our Islamic duty," said Sheik Ali Mohamud Rage, a group spokesman in Mogadishu.

An American aid worker was also killed and six members of a Pennsylvania church group were seriously wounded in the blasts, which targeted an outdoor rugby field and a packed Ethiopian restaurant in Kampala.

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

Al-Shabab commander Yusuf Sheik Issa rejoiced in the bombings, which mark the first time the group has reached out beyond the borders of Somalia, where the militia has seized control of large swathes of territory and established a strict and brutal form of Islamic law in its wake.

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"Uganda is one of our enemies. Whatever makes them cry, makes us happy. May Allah's anger be upon those who are against us," Sheik said.

Nate Henn, a Wilmington, De., native who was working with Uganda's child soldiers, was among the dozens killed while watching the soccer match on a large TV set up on the outdoor rugby field.

Henn, 25, was remembered as a tireless and devoted activist by the California-based aid group Invisible Children, which sponsored his work in Uganda.

"He sacrificed his comfort to live in the humble service of God and of a better world, and his is a life to be emulated," the group said in a statement on its website.

Six missionaries from the Christ United Methodist Church in Selingsgrove, Pa., were injured in the blast at the Ethiopian restaurant. Five had stayed behind in Uganda to complete their mission work after their friends returned home just days ago.

The group arrived at the Ethiopian restaurant early to get good seats for the game, said group leader Lori Ssebulime, who is married to a Ugandan. Ssebulime described the injuries of 16-year-old Emily Kerstetter, who was seriously injured in the blast.

"Emily was rolling around in a pool of blood screaming," said Ssebulime, who has helped bring in U.S. church groups since 2004. "Five minutes before it went off, Emily said she was going to cry so hard because she didn't want to leave. She wanted to stay the rest of the summer here."

The State Department said that only five American citizens from the church group had been injured, though it was not immediately clear whether the discrepancy was due to the lighter nature of Ssebulime's injuries.

The blasts came just two days after a Shabab commander called for militants to attack sites in Uganda and Burundi, two nations that contribute troops to the African Union peacekeeping force in Somalia.

The attacks on two soft targets filled with civilians raised concerns about the capabilities and motives of al-Shabab, which the U.S. State Department has declared a terrorist organization.

They appear to represent a dangerous step forward by al-Shabab, analysts said, and could mean that other East African countries working to support the Somali government will face attacks.

"Al-Shabab has used suicide bombers in the past and shown no concern about civilian casualties in its attacks," said David Shinn, a former U.S. ambassador to Ethiopia and a professor at George Washington University. "Some elements of al-Shabab have also prohibited the showing of television, including the World Cup, in Somalia."

Ugandan President Yoweri Museveni toured the blast sites Monday and said that 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-Shabab, which wants to overthrow Somalia's weak, U.N.-backed government, is known to have links with Al Qaeda. Al-Shabab also counts militant veterans from the Iraq, Afghanistan and Pakistan conflicts among its ranks. Their fighters also include young men recruited from the Somali communities in the United States.

Ethiopia, which fought two wars with Somalia, is a longtime enemy of al-Shabab and other Somali militants who accuse their neighbor 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.

President 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.

Sunday's terror attacks are not the first to hit East Africa. U.S. Embassies in Nairobi, Kenya, and Dar es Salaam, Tanzania, were the targets of deadly twin bombings by Al Qaeda in 1998, killing 224 people including 12 Americans. An Israeli airliner and hotel in Mombasa, Kenya, were targeted by terrorists in 2002.

The United States worries that Somalia could be a terrorist breeding ground, particularly since Osama bin Laden has declared his support for Islamic radicals there.