Breast bombs which blow up on board midair flights have sparked fears of a new front in the war on terror.

Al-Qaida is developing exploding breast implants which cannot be detected by scanners and security staff at airports, according to intelligence reports.

They can be activated by being injected with a liquid or an electrical signal and have triggered a security alert at Heathrow airport in London.

Bomb expert Andy Oppenheimer told the Mirror: "There is a great fear that al-Qaida is planning on using internal devices to try to get through airport scanners. These explosives could be in breast implants."

Analysts believe that the preferred substance for so-called "intimate bombs" is Pentaerythritol tetranitrate, or PETN. They said that security fears over the devices were already leading to longer queues at airports.

PETN was used by the "underpants bomber" Umar Abdulmutallab when he tried to blow up a plane on Christmas Day, 2009. Abdulmutallab, who was a student in London, used an explosive device hidden in his pants containing PETN. Al-Qaida in the Arabian Peninsula claimed that it supplied the bomb.

The deadly potential of PETN was illustrated by terrorists who used it to kill 13 people in a bomb attack on a courthouse in Delhi in 2011.

A member of security staff at Heathrow said: "There are genuine fears over this. We have been told to pay particular attention to females who may have concealed hidden explosives in their breasts.

"This is particularly difficult for us to pick up but we are on a very high state of alert. It's led to long queues here at Heathrow - much longer than usual at this time of the year."

The breast bomb scare marks a new development in terror group attempts to beat airport security. Al-Qaida in Yemen has already developed an odourless liquid which is highly flammable and can be applied to clothing with little chance of detection.

Independent security analyst Paul Beaver said: "There are deeply serious concerns over body cavities and implants of all kinds - including breast implants - being used to hide explosives.

"It is taking longer to get through Heathrow and other airports in Europe and North America because of these fears."

A Heathrow spokesman refused to comment when contacted by IBTimes UK.