Somalia's al Shabaab says Uganda did not prevent attack by the group

(Reuters) - Somalia's al Shabaab militants denied on Monday that Ugandan authorities had foiled an attack by the group, after police in Uganda's capital seized explosives and suicide vests and arrested 19 people. Ugandan Information Minister Rose Namayanja told Reuters that Saturday's raid seized an extraordinary amount of explosives from a suspected al Shabaab cell that was planning an attack. Namayanja said the government believed the Kampala cell had links to al Shabaab, without elaborating.

On Saturday, the U.S. Embassy in Uganda asked its citizens to seek safety, saying that local authorities had uncovered a "terrorist cell" run by al Shabaab, which the United States believed was preparing for an attack.

"Harakat Al-Shabaab Al-Mujahideen strongly deny the purported claim by the ... United States and their subordinate Ugandan officials that they've foiled an attack that was supposedly being planned in Uganda by the Mujahideen," sheikh Ali Mohamud Rage, the spokesman of al Shabaab, said in a statement released on Monday.

Ugandan authorities say they have increased security at hotels and other key sites, including Entebbe International Airport, since making the arrests.

On Monday, Dan Travis, a Public Affairs Officer at the U.S. Embassy in Kampala, said without giving more details that the United States had helped the Ugandan government during the raid.

"All I can say is that we were asked by the Ugandan authorities to lend support and we did lend support but I can't discuss the nature of that support," he told Reuters.

The al Qaeda-allied militants carried out a dramatic attack nearly a year ago on the upscale Westgate shopping mall in Nairobi that killed 67 people. It also carried out attacks in sports bars where people were watching the soccer World Cup on television in the Ugandan capital of Kampala in 2010, leaving left 74 dead and dozens more injured.

Al Shabaab - which wants to impose its own strict version of Islam - has threatened more attacks since the killing of their leader, Ahmed Godane, in a U.S. strike earlier this month.

The group controlled Mogadishu and the southern region of Somalia from 2006 to 2011. It was driven out of the capital by peacekeeping forces deployed by the African Union.

The African Union forces opened a new offensive this year to push the Islamists out of towns and other areas they still control. Several centres have been retaken, but al Shabaab remains in control of some towns and swathes of countryside.