Officials in Uganda say Somalia's al-Qaida-linked al-Shabab rebel group is suspected of carrying out Sunday's twin bombings in the capital Kampala. The blasts killed more than 60 people and left dozens of others wounded. The group has previously threatened to attack Uganda and Burundi for sending troops to Somalia as part of an African Union peacekeeping mission.

Police in Kampala say the blasts tore through crowds watching the final World Cup soccer match in two of the busiest parts of the city.

The first explosion ripped through an Ethiopian restaurant in Kabalagala, a Kampala suburb popular with ex-patriots and foreign visitors. The second blast occurred at the Kyadondo Rugby Club in the center of town, where a huge crowd had gathered to watch the game between Spain and the Netherlands on giant TV screens.

Nearly 50 people are believed to have been killed at the Rugby Club. At least 15 died in the restaurant explosion.  A U.S. embassy spokeswoman in Kampala, Joann Lockard, says one American is among the dead and several others may have been wounded.

"We have had one American citizen fatality. I am hoping to be able to have additional information about American citizen injuries," Lockard said.

Related video clip of Uganda attack:

The Ugandan government says it is looking into the possibility that two suicide bombers wearing vests may have carried out the attacks. Security officials had earlier speculated that the bombs had been planted at the two sites and set off remotely.  

The Ugandan army declined to comment. But the inspector general of the Ugandan police, Kale Kayihura, linked the bombings to recent threats by Somalia's al-Shabab militants against countries contributing troops to the African Union peacekeeping mission in Somalia.    

More than 6,000 troops from Uganda and Burundi are in the Somali capital, Mogadishu, protecting key installations and the U.N.-backed Transitional Federal Government from attacks by al-Shabab and other Islamist insurgents. The leaders of East Africa's regional bloc, IGAD, have also pledged to send 2,000 additional troops to bolster the peacekeeping force.

Last week, al-Shabab's top leader, Ahmed Abdi Godane, accused African Union troops of continuing to kill civilians in the Somali capital, Mogadishu. He said his group would seek revenge.

Al-Shabab, considered a terrorist group by the United States and other western countries, has already carried out several suicide attacks against peacekeepers in Somalia.

Kampala resident Naboth Muhereza says that Ugandans are in deep shock and concerned about their safety.

"Everyone is worried, wondering why and who penetrated, who did this," said Muhereza. "There are speculations that it is al-Shabab that attacked Uganda because Uganda has got some soldiers in Somalia. So, they are revenging by killing Ugandans."

The President of Somalia's Transitional Federal Government Sharif Sheik Ahmed sent condolences to the victims' families in Uganda and said the region and the international community will not tolerate the spread of insecurity by terrorists.