US authorities have been warned of a specific terrorist threat to Entebbe Airport in Uganda Thursday night.

The US embassy in Kampala said Ugandan police had informed them that intelligence sources believe there is a threat to the airport from an unknown terrorist group.

In a statement the embassy said the threat was apparently aimed for "today, July 3rd, between the hours of 2100-2300".

It added: "Individuals planning travel through the airport this evening may want to review their plans in light of this information.

"US Embassy Kampala wishes to remind US citizens of the continued threat of potential terrorist attacks in the country."

The statement said the targets could include "hotels, restaurants, nightclubs, shopping malls, diplomatic missions, transportation hubs, religious institutions, government offices, or public transportation".

The alert comes after security at British airports was increased following warnings from the US that terrorists are developing bombs that can be smuggled on to planes without detection.

US Homeland Security chief Jeh Johnson said he had asked officials to "implement enhanced security measures in the coming days at certain overseas airports with direct flights to the United States".

A statement issued by the US Department for Homeland Security said: "We are sharing recent and relevant information with our foreign allies and consulting the aviation industry.

"These communications are an important part of our commitment to providing our security partners with situational awareness about the current environment and protecting the travelling public."

Transport Secretary Patrick McLoughlin said the additional security was not expected to cause "significant" disruption to flights.

He told Sky News: "There will be extra security checks but they will be made in the course of events people already go through and I hope there will not be significant delays."

But British aviation security expert Philip Baum said heightened security will inevitably mean longer queues and increased waiting times to board flights at UK airports.

"It will mean an increase in the number of random searches, secondary searches and an increase in the number of passengers asked to remove shoes and possibly all passengers being asked to remove shoes if they’re going on certain flights," he said.

US officials said their security warning followed intelligence reports that Islamist groups in Yemen and Syria had joined forces to prepare an attack on the US.

Bomb-makers from al Nusra Front, al Qaeda's affiliate in Syria, and Yemen-based al Qaeda in the Arabian Peninsula (AQAP) are believed to be working together to develop the new devices.

According to ABC News, they are trying to build non-metallic bombs that could evade metal detectors.

As a consequence security enhancements are likely to include greater scrutiny of US-bound passengers' electronics and footwear and installation of additional bomb-detection machines.

Sky's US correspondent Dominic Waghorn said US officials were also closely monitoring the Islamic State in Iraq and Syria (ISIS) over fears its success in Iraq might help it recruit jihadists from Europe, who would have easier access to flights bound for US cities.

-Adapted from SkyNews