The US Transportation Security Agency (TSA) has revised a policy which had previously allowed travellers to avoid going through an electronic body scanner in favour of a physical search at airports across the US.

In a document updating the policy last Friday (Dec 18) - just days before the busy festive period - TSA announced it would now require some passengers to undergo compulsory full-body scans.

TSA's announcement comes amid heightened concerns over security in the aviation sector and possible terror plots.

"Generally, passengers undergoing screening will still have the option to decline a (full-body) screening in favour of physical screening," the TSA said in a post on Twitter.

"However, some passengers will be required to undergo (full-body) screening if warranted by security considerations in order to safeguard transportation security."

The agency added that such cases will not happen very often and the "vast majority of passengers will not be affected".

The screening, which is known as "advanced imaging technology", allows TSA to detect non-metallic weapons - such as the plastic explosives hidden in the underwear of a man who wanted to detonate a bomb on board a plane on Christmas Day in 2009 - and liquids.

However, the body scanners do not have the ability to store images. They also use a generic image of a human body instead of the person being screened.