Ugandan security forces have claimed to have foiled an imminent al-Shabab 'terror' attack inside the capital Kampala, as the US has warned its citizens to seek shelter amid anti-terror operations.

"Joint security agencies in Uganda have foiled a terrorist attempt at one of its installations ... we have made arrests," police spokesman, Fred Enanga, told the AFP news agency.

The US embassy said on Saturday that Ugandan security forces discovered an "al-Shabab terrorist cell," planning an "imminent attack".

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"At this point we are not aware of specific targets, and the Ugandan authorities have increased security at key sites, including Entebbe international airport," the embassy said in a statement.

"All US citizens are advised to stay at home or proceed to a safe location. Shelter-in-place and await further guidance," it added.

On Monday, the US embassy warned of possible revenge attacks by Somalia's al-Qaeda linked al-Shabab fighters, after a US airstrike killed the group's leader, Ahmed Godane. 

Under Godane's leadership, al-Shabab established a foothold in most parts of Somalia and carried out attacks in Kenya, Uganda and Djibouti.

The US has said possible targets for attacks "could include hotels, restaurants, nightclubs, shopping malls, diplomatic missions, transportation hubs, religious institutions, government offices, or public transportation".

During the 2010 World Cup final, twin bombings in Kampala killed 76 people after explosions ripped through two busy restaurants.

Al-Shabab claimed reponsibility for the blasts, citing Uganda's decision to sent troops to Somalia as part of an African Union force.

Source: Agencies