"Joint security agencies in Uganda have foiled a terrorist attempt at one of its installations," police spokesman Fred Enanga said. "We have made arrests."
He gave no further details, and it was not immediately possible to determine the target of the reported attack, or at what stage it had been stopped.
The US embassy issued a warning to its citizens in the east African nation.
"Ugandan authorities are conducting operations against a suspected terrorist cell in Kampala," 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."
Uganda's Ministry of Internal Affairs said immigration officers had carried out an "operation on illegal immigrant workers in different parts of Kampala" today morning, with 69 people arrested.
It was not clear if the raids were connected. Last Monday the US embassy warned Somalia's
Al-Qaeda-linked Shebab insurgents may try to exact revenge for a US air strike that killed the militant group's commander.
"Stay alert to the ongoing potential for terrorist attacks in Uganda," it said.
"We also caution US citizens of the possibility of retaliatory attacks in Uganda by Al-Shebab in response to the US and Ugandan military actions in Somalia last week which killed Al-Shebab leader Ahmed Godane."
Uganda's government said the country -- a major contributor to AMISOM, the African Union force fighting the Shebab -- was "happy" at death of Godane, and had provided the US with key intelligence on his whereabouts.

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