* Ugandan aviation authority confirms threat
* Uganda hit by Somali-linked militants in past
* No nonstop flights from Uganda's Entebbe to U.S. (Adds comments from police, background on U.S. concerns)
By Elias Biryabarema
KAMPALA, July 3 The United States warned its citizens in Uganda on Thursday about a "specific threat" of an attack within hours on Entebbe International Airport, which is near the capital Kampala, according to a message on the U.S. Embassy website.
It said information from Uganda's police indicated that the attack could take place between 9 p.m and 11 p.m. local time (1800 GMT and 2000 GMT) on Thursday, adding that citizens planning to travel at that time might consider reviewing their arrangements.
As one of the countries that contribute forces to an African Union peacekeeping mission battling the Islamist militant group al Shabaab in Somalia, Uganda has suffered militant attacks in recent years, and al Shabaab has threatened more.
A spokesman for Uganda's Civil Aviation Authority, Ignie Ugundura, confirmed the authority had issued an alert on Wednesday that "informed the airport community", but did not give details.
A Ugandan police spokeswoman said security had been stepped up at Entebbe, but that the police were not aware of a specific threat to Uganda.
The U.S. Embassy message said it had "received information from the Uganda Police Force (UPF) that according to intelligence sources there is a specific threat to attack Entebbe International Airport by an unknown terrorist group today, July 3, between the hours of 2100-2300".
The U.S. Embassy has issued other alerts during the year about possible attacks in Uganda, which it says faces a "continued threat".
American authorities said on Wednesday they would require increased security at overseas airports with nonstop flights to the United States. U.S. officials cited concerns that al Qaeda operatives in Syria and Yemen were developing bombs that could be smuggled onto planes.
There are no nonstop flights from Uganda's Entebbe airport to the United States.
Al Shabaab, which is aligned with al Qaeda, attacked a shopping mall in Nairobi, capital of neighbouring Kenya, last year and in 2010 bombed sports bars in Uganda where people were watching the soccer World Cup on television. Dozens were killed in both attacks.
Entebbe airport is known as the scene of an Israeli special forces operation in 1976 to rescue more than 100 Israeli and Jewish passengers who were being held hostage on board an Air France plane by Palestinian and German guerrillas. (Writing by Edmund Blair; Editing by Kevin Liffey)