The Somali Islamist group al-Shebab has claimed responsibility for the overnight bomb blasts in the Ugandan capital Kampala that killed at least 74 people.

"We are behind the attack because we are at war with them," Ali Mohamoud Rage, the group's top spokesman told reporters in Mogadishu.

In an audio message earlier this month the group said that Uganda would face retaliation for its role in supporting the western-backed Somali transitional government.

"We had warned the Ugandans to refrain from their actions, we spoke to the leaders and we spoke to the people and they never listened to us," Rage said.

Meanwhile, the global police agency Interpol has said it will send a team to Uganda to assist local officers.

Interpol Secretary General Ronald Noble branded the attack on Kampala football fans "despicable and cowardly" and said that Ugandan police chief Kale Kayihura had requested assistance.