The US embassy in Uganda warned Thursday of a "specific threat" by an unknown group to attack Entebbe international airport, which serves the capital Kampala.

The alert came as travellers flying to the United States from Europe and the Middle East faced tighter security because of new concerns about the development of explosives that could circumvent airport security.

"The US embassy has received information from the Uganda police force that according to intelligence sources there is a specific threat to attack Entebbe International Airport by an unknown terrorist group today, July 3rd, between the hours of 2100-2300 (1800 GMT to 2000 GMT)," the statement said.

Although it did not name any group, Al-Qaeda linked Al Shabaab insurgents have claimed recent attacks in Kenya and Djibouti, and at home in Somalia.

Uganda has troops in Somalia as part of the African Union force fighting the Al Shabaab and is on high alert amid fears of attacks by the Islamist militants.

Army spokesman Paddy Ankunda said troops had been deployed at the airport and in the capital, some 35 kilometres (20 miles) from Entebbe.

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"People must be vigilant in the face of this threat, report any suspicious individuals seen in their areas," he said, calling on people to "stay calm and alert."

The US embassy suggested people planning travel through the airport during Thursday evening should review their plans in light of the warning.

Army deployed

It also warned its citizens of a general threat of attacks which could target hotels, restaurants, clubs, malls, diplomatic missions, government buildings and transport.

But government spokesman Ofwono Opondo said the US was being "over sensitive in their warning", and urged people to continue with travel plans as normal.

"All the security measures have been taken," he said. "We encourage people to go on with their business."

Al Shabaab claimed responsibility for the assault on the Westgate shopping centre that killed at least 67 people in the Kenyan capital of Nairobi in September last year as well as for two night time attacks on the Kenyan coast last month that killed around 60 people.

In May, a male and female suicide bomber blew themselves up in an attack on restaurant popular with Westerners in central Djibouti, killing a Turkish national.

Entebbe's airport, on the shores of the vast Lake Victoria, was the site of the daring 1976 raid by Israeli special forces, to free hostages kidnapped on board an Air France aircraft by Palestinian and German gunmen.

Last month the US warned citizens of the threat of attacks during televised screenings of the World Cup.

READ: US warns of terrorist threat to Uganda churches

During the World Cup final four years ago, Somalia's Al Shabaab insurgents killed at least 76 people after setting off explosions that ripped through two restaurants in the Ugandan capital.

Police spokesman Fred Enanga insisted the "airport is very safe and secure", but added that security had boosted across the capital.

"We are at a very crucial stage because of the World Cup events held in town," he said.

In Somalia, the Al Shabaab have warned that violence will intensify during Islam's holy month of Ramadan, carrying out a string of bomb attacks and killings.

On Thursday, they claimed responsibility for shooting dead a lawmaker and his bodyguard.