"The threat information indicates a group of attackers may be preparing to strike places of worship in Kampala, particularly churches, including some that may be frequented by expatriates, in May or June," the embassy warned in a statement to US citizens yesterday.
No specific group was mentioned in the warning, but Somalia's Al-Qaeda linked Shebab insurgents or their supporters have been blamed for a string of attacks, especially in neighbouring Kenya.
Both Uganda and Kenya are key contributors of troops to the African Union force fighting the Shebab in Somalia, and the Islamists have carried out major attacks in both countries in retaliation in the past.
Shebab bombers killed at least 76 people in Uganda's capital Kampala in 2010.
Uganda set up a specialist tourism police force in March as part of counter-terrorism measures, amid warnings of Shebab attacks.
The United Nations has also warned of an increased threat of attacks from the Shebab following a major offensive launched against the militants in March.