Intelligence experts are warning that drone attacks could be used by terror groups like the Islamic State (ISIS) and al-Qaeda to target major sporting events in Europe and the U.S.

According to them, it is "only a matter of time'' before ISIS terrorists unleash drone attacks on global stadiums. They fear the attack could be deployed by sleeper cells or lone wolves who have been brainwashed by ISIS or al-Qaeda terrorists.

''ISIS are already using drones in Iraq and Syria for intelligence gathering, quite successfully for battlefield awareness,'' Chris Abbott, the group's chief executive, told the Daily Beast.

''They are in direct competition now with al-Qaeda and are desperate to launch a mass casualty attack on Western targets,'' he added.

According to Abbott, ISIS's ''sophisticated'' use of propaganda also allows the terror group to use drones that could fit in with cameras to film the attacks taking place.

Abbott's team has been analysing the potential threat of large number of small ''off-the-shelf'' drones on the market and found that "there is no single counter measure that could prevent such attacks.''

He stressed that the defence starts with "regulating who can own a drone."

"Unfortunately if you have to resort to shooting them out of the sky in an urban environment or at a packed stadium the risk of collateral damage is very high,'' he said.

The chief executive also noted that even a small drone, capable of carrying up to 10 kg of explosives or a suicide vest, could be lethal if directed at a high profile target such as a politician.

Last month fears were raised that drones could be used by the terror group to target British Prime Minister David Cameron. In 2013, a drone operated by the German Pirate Party landed near German Chancellor Angela Merkel as she addressed a supporters' rally in Dresden, according to reports.

In October 2014, a football match was also abandoned after activists reportedly flew a drone carrying an nationalist flag over the pitch. And last April, a drone carrying radioactive sand from the Fukishima nuclear plant landed on top of the Japanese prime minister's offices in Tokyo.

Abbott urged authorities to regulate those who own drones and to pick up the movement of suspicious individuals who have purchased or acquired drones to avoid an attack.