Ugandan police have found an unexploded suicide vest and arrested six of the more than 20 Somalis and Ugandans suspected of planning twin bombings that killed 76 soccer fans on Sunday, an intelligence source said.
Somali al Shabaab Islamists linked to Al Qaeda said on Monday they had carried out the attacks on a crowded restaurant and a rugby club in the capital Uganda while fans watched the World Cup final on television.
An official from the group said on Tuesday there had been no suicide bombers involved in the attack on Uganda, which has peacekeepers in Somalia.
A Ugandan military intelligence source told Reuters on Tuesday that intelligence officials had received a tip-off last month that an attack was being planned.
"On June 17 an informer from the Kisenyi suburb of Kampala told intelligence that some Somalis were planning an attack during the World Cup," the source said.
The official said more than 20 people, Somalis and Ugandans, were involved in planning the attacks. "So far we have arrested six people from that racket," he said.
Al Shabaab has threatened more attacks unless Uganda and Burundi withdraw their peacekeepers from the African Union (AU) peacekeeping force in Somalia (AMISOM), where the militants are fighting the government and control large parts of the country. Police said the suicide vest found late on Monday at a third site was designed so it could also be planted, rather than worn.
"Rage blessed those who carried the attack and expected a long life for them. That shows there was no suicide bomb. These were planted," a man who identified himself as Yonis, assistant to al Shabaab spokesman Sheikh Ali Mohamud Rage, told Reuters.
Al Shabaab has banned watching soccer matches in areas under its control and the bombing of people watching Sunday's final World Cup match while drinking alcohol was a double whammy for the rebel group -- killing unbelievers while taking revenge for what is seen as an invasion by Ugandan troops.
Coordinated attacks are a hallmark of Al Qaeda and groups linked to Osama bin Laden's militant network. If confirmed to be the work of al Shabaab, it would be the first time the militants have taken their push for power internationally.
The African Union said Uganda would still host a summit of African leaders this month and said it would not be deterred from its peacekeeping mission.
"The government of Uganda added there will be no danger to visiting heads of state and dignitaries ... The AU summit will not be disturbed by this incident," Noureddine Mezni, spokesperson for AU commission chairman Jean Ping told Reuters.
Regional bloc IGAD also said it would not be cowed and would continue to support the Western-backed government in Somalia.
"We shall continue with our plans to increase peacekeepers in Somalia to over 8,000 and we hope to have the extra troops in the country by the second week of August," executive secretary Mahboud Maalim told journalists in the Kenyan capital Nairobi.
Last week IGAD members Kenya, Uganda, Sudan, Ethiopia, Somalia and Djibouti said they eventually wanted 20,000 troops from the AU and United Nations deployed in Somalia. Uganda's opposition Forum for Democratic Change (FDC) party urged President Yoweri Museveni to pull his peacekeepers out and said it planned a withdrawal if it won elections in 2011.
"There is no peace to keep in Somalia and Uganda has no strategic interest there. We're just sacrificing our children for nothing," FDC spokesman Wafula Oguttu told Reuters.
Analysts say any sustained bombing campaign would damage Uganda's investment climate, but a one-off attack was unlikely to deter major companies such as British hydrocarbons explorer Tullow Oil from investing.
Foreign direct investment into east Africa's third largest economy has surged, driven by oil exploration along the western border with Democratic Republic of Congo.
One American was among the dead. The U.S. embassy in South Africa said five other U.S. citizens who had been wounded had been evacuated to Johannesburg and Nairobi. An FBI team is in Kampala, the U.S. State Department said.
There has been mixed reaction in Somalia, with many apologetic for the loss of lives while others rejoiced.
"Uganda and Burundi troops are carrying out genocide with every shell they launch in Mogadishu," said clan elder Yusuf Abdiqadir Maalim in Kismayu. "It is good for them to see and taste the pain of a massacre."