Officials in the US have ordered overseas airports that have direct flights to the country to heighten security measures. That includes enhanced screening of electronic devices, such as smartphones, tablets and laptops.

And as travellers may be required to switch on their devices to prove they are real, it is warned that powerless devices will not be allowed on board. If you have no battery life in your phone, for example, you will either have to abandon it or not catch your flight.

London Heathrow is believed to be one of the overseas airports implementing the measures.

The US announced that security measures would be intensified last week, with no official details as to why. Although analysts claim that they are in response to intelligence that Islamic militants in Syria and Yemen may have developed bombs that are not detectable by airport security.

"During the security examination, officers may also ask that owners power up some devices, including cell phones," said the Transportation Security Administration.

"Powerless devices will not be permitted onboard the aircraft. The traveller may also undergo additional screening."

Today, 7 July, is the ninth anniversary of the 7/7 London bombings that claimed 52 lives in the capital.