KAMPALA, Uganda — At least three bombs exploded Sunday in a synchronized attack on large gatherings of World Cup soccer fans watching the televised final on outdoor screens in this normally peaceful capital, turning a boisterous night of cheering into scenes of death and panic. The police and witnesses said more than 50 people were killed, including some foreigners, among them at least one American.

The bombs struck at 10:30 p.m. local time in the middle of the match between Spain and the Netherlands under way in South Africa, hitting a popular Ethiopian garden restaurant and a large rugby field in a different Kampala neighborhood where hundreds of people had massed to watch the game.

Ugandan police officials said they suspected that the Shabab, a militant Islamic group in nearby Somalia, might have been behind the bombings. If so, it would be that group’s first attack outside Somalia. But the police said it was premature to draw conclusions.

“We can’t rule anything out,” said Kale Kayihura, Uganda’s police inspector general, at the scene of one of the attacks. “This was obviously terrorism, from the way it was targeted at World Cup watchers in public places.”

Joan Lockard, a spokeswoman at the American Embassy in Kampala, confirmed that at least one American was killed. She did not identify the victim.

Local journalists at a major hospital said an unidentified number of American citizens were among the wounded.

The Shabab, one of the more fearsome militias vying for power in Somalia, ban music, dancing and sports, have links to Al Qaeda and have repeatedly threatened targets in Uganda as well as in Burundi because both countries contribute to the African Union peacekeeping mission in Somalia, a lawless nation in the Horn of Africa.

The police said other suspects were former rebels in the neighboring Democratic Republic of the Congo with connections to Uganda.

The Ugandan capital is relatively safe and relaxed compared with other big cities in Africa, and such bombings are extremely rare. But the city turned tense and fearful early on Monday, as military vehicles and ambulances screeched through the streets and Kampala’s bars and clubs emptied.

At the Ethiopian restaurant that was attacked, an outdoor cafe with lawn tables known as the Ethiopian Village, soldiers and onlookers watched side by side as rescue crews extracted the dead and the wounded from the wreckage. The police said the bomb appeared to have been placed under a dining table where a group of foreigners, including some Americans, had been sitting.

At least 15 people were killed in that blast, police officials and witnesses said.

“It was so loud,” said a woman named Mami, one of the owners of the restaurant, which had become popular with soccer fans because it showed the games on an outdoor screen. “I am so confused. My God. My God. My God.”

At the rugby field where fans had gone to watch the final game on a large screen, the police and witnesses said they counted at least 44 bodies. Lines of chairs had been blown apart. One middle-aged woman sat dead, her head hung back, blood dripping.

“We were just watching football when the two bombs went off,” said Brian Bomakech, a Ugandan fan at the field. “So many people were hurt, so many people have died.”

In Mogadishu, the Somalian capital, Sheik Yusuf Sheik Issa, a Shabab commander, was quoted by The Associated Press early Monday as saying he was happy with the attacks in Uganda. The sheik refused to confirm or deny any responsibility by the Shabab.

“Uganda is one of our enemies,” The A.P. quoted him as saying. “Whatever makes them cry, makes us happy. May Allah’s anger be upon those who are against us.”

The bombings came two days after another Shabab commander, Sheik Muktar Robow, called during Friday Prayer in Somalia for militants to attack sites in Uganda and Burundi.

In Washington, a White House spokesman, Tommy Vietor, said late Sunday that the United States was prepared to provide assistance to Uganda.

“The president is deeply saddened by the loss of life resulting from these deplorable and cowardly attacks, and sends his condolences to the people of Uganda and the loved ones of those who have been killed or injured,” he said.