KAMPALA (Reuters) - Somali Islamists said on Monday they had carried out two bomb attacks in Uganda that killed 74 soccer fans watching the World Cup final on television.
The explosions in the closing moments of Sunday's match ripped through a crowded restaurant and a rugby club in the capital Kampala.
Al Shabaab militants in anarchic Somalia had already threatened to attack Uganda for sending peacekeeping troops to prop up its fragile, Western-backed government.
In Mogadishu, the group threatened more attacks unless Uganda and Burundi withdrew their peacekeepers.
"Al Shabaab was behind the two bomb blasts in Uganda," spokesman Sheikh Ali Mohamud Rage told reporters.
"We are sending a message to Uganda and Burundi: If they do not take out their AMISOM troops from Somalia, blasts will continue, and it will happen in Bujumbura too."
Al Shabaab is fighting the Somali government and claims links with al Qaeda.
"At one of the scenes, investigators identified a severed head of a Somali national, which we suspect could have been a suicide bomber," said army spokesman Felix Kulayigye. "We suspect it's al Shabaab because they've been promising this."
Inspector General of Police Kale Kayihura said some arrests had been made, but gave no details. He said police had begun reviewing security in public places.
Burundi, which also contributes troops to the peacekeeping mission, stepped up security, said an army spokesman in the capital, Bujumbura.
The dead included one American. President Barack Obama condemned what he called cowardly attacks, and the White House said the Federal Bureau of Investigation would help in the investigation.
One bomb targeted the Ethiopian Village restaurant, a popular night-spot that was heaving with soccer fans and is frequented by foreign visitors. The second attack struck the Lugogo Rugby Club, which was also showing the match.
Coordinated attacks have been a hallmark of al Qaeda and groups linked to Osama bin Laden's militant network.
Among the dead were at least 60 Ugandans, an Irish woman, and 11 Ethiopians and Eritreans. Two had not been identified.
The U.S. State Department said one American citizen was killed and five injured. The U.S. charity Invisible Children said one of its members, Nate Henn from Wilmington, Delaware, had been killed in the rugby club blast.
Ugandan President Yoweri Museveni visited the rugby club.
"This shows you the criminality and terrorism that I have been talking about," he said. "If you want to fight, go and look for soldiers, don't bomb people watching football."
Bereket Simon, the Ethiopian government's head of information, called the attacks a "cowardly act by al Shabaab terrorists."
Ethiopian troops invaded Somalia in 2006 to oust an Islamist movement. That sparked the Islamist insurgency that rages today.
The blasts came near the end of the match and left shocked survivors reeling among corpses and scattered chairs.
"We were watching soccer here and then, when there were three minutes to the end of the match, an explosion came ... and it was so loud," witness Juma Seiko said at the rugby club.
Heavily armed police cordoned off both blast sites and searched the areas with sniffer dogs while dazed survivors helped to pull the wounded from the wreckage.
Uganda, east Africa's third largest economy, is attracting billions of dollars of foreign investment, especially in its oil sector and government debt markets.
But investors in Uganda and neighboring Kenya, which shares a porous border with Somalia, often say the threat from Islamic militants is a serious concern.
"I certainly think the blasts will make risk appraisals tighter on Uganda. If it does transpire to be al Shabaab, that will certainly raise the concerns of Western investors and also Chinese investors in Uganda," said Alex Vines, Head of Africa Programmes at London's Chatham House think-tank.
The Ugandan shilling fell slightly against the dollar on Monday.
Somali residents of Kampala said they feared a backlash.
"We are in fear and locked in our homes today," said Bisharo Abdi, a Somali refugee. "Some Ugandans are saying 'Kill Somalis'."
On Saturday, Somali President Sheikh Sharif Ahmed told Reuters the growing number of foreigners joining the Islamic insurgents posed a threat to regional security.
Additional reporting by Frank Nyakairu, Sahra Abdi and Abdi Guled in Nairobi; Editing by Kevin Liffey