Ugandan police stepped up security in the capital Kampala following a "specific threat" of a planned attack on its main international airport.
The US embassy warned of a threat to attack Entebbe airport between 21:00-23:00 (18:00-20:00 GMT), but no incidents were reported in that time.
The army said troops had been deployed at the airport and in the city.
Militant Islamists al-Shabab bombed two Kampala restaurants during the 2010 football World Cup, killing 70 people.
On Thursday, the US advised its citizens to review plans to travel through Entebbe International Airport.
The airport's security unit later said in a widely publicised document: "According to intelligence sources, there is a specific threat to attack Entebbe International Airport by an unknown terrorist group... Such a threat cannot be taken lightly."
Army spokesman Paddy Ankunda said troops had been deployed at the airport and in the capital, about 35km (20 miles) from Entebbe.
"People must be vigilant in the face of this threat, report any suspicious individuals seen in their areas," he said.
He called on people to "stay calm and alert".
A reporter with AFP news agency said there was a heavy security presence in Kampala, with soldiers marching along city streets.
Security forces also erected barriers and closed some roads, Uganda's Daily Monitor newspaper reports.
Several international conferences were taking place in the city and the security forces wanted to make sure that visitors were safe, Kampala Metropolitan Police spokesman Patrick Onyango is quoted as saying.