It has been reported that the Somali militant group al-Shabaab claimed responsibility on Monday for three bombings that killed at least 74 people in Uganda's capital.

CNN has reported that Ali Mohamoud Rage said at a news conference in Mogadishu, Somalia, "We are behind the attack because we are at war with them."

"And the best of men have promised and they have delivered ... We wage war against the 6,000 collaborators; they have received their response," al-Shabaab's press office said in a statement obtained by CNN.

The 6,000 is apparently a reference to the number of African Union peacekeepers in Somalia, a group to which Uganda contributes, CNN has said.

The three bombings occurred Sunday in two Kampala neighborhoods where soccer fans were watching the World Cup final match.

It has also been reported that Ugandan President Yoweri Museveni declared a week of national mourning, beginning Tuesday.

Museveni will inspect the explosion sites, his office's media center said Monday in a statement.

The media center said, "The public is reminded to be vigilant in regards to security and report any suspicious activities to the police. Investigations are ongoing and further information shall be availed later today."

The media center further added that officials confirmed numerous deaths in explosions at venues in Kampala Sunday during the televised World Cup finals. Dozens of people were admitted to hospitals and many were treated for minor injuries and released. (With Inputs from Agencies)