Intelligence sources revealed on Sunday that Britain's secret listening centre picked up "chatter" of people with "Birmingham and London accents" celebrating the crash of a Russian airliner in Sinai last week immediately following the disaster that killed all 224 people on board.
This appeared to indicate that British extremists with links to jihadist groups like the Islamic State (ISIS) could have a hand in the downing of the Airbus A321M Metrojet passenger aircraft over the Sinai peninsula in Egypt on Oct. 31, the Sunday Express reported.
The regional accents suggest "a definite and strong link" between British extremists and the attack, the intelligence sources at the Government Communications Headquarters (GCHQ) in Cheltenham said.
"Jihadis in the Sinai area of Egypt could be heard celebrating," one source told the Express, adding that "a closer analysis of that material has identified London and Birmingham accents among those numerous voices."
"There has also been some Internet traffic suggesting that there was British involvement in the attack. This was a very sophisticated, carefully planned operation involving many moving parts," the source said.
"We know there are British jihadis in Egypt fighting with members of Islamic State. They were trained in Syria and are now hardened terrorists. Some of the Britons have an electronics background and have been developing some very sophisticated bombs.
"They have been experimenting with different-sized charges and different types of explosives but there was nothing prior to this attack to suggest that they were going after airlines," the source added.
The sources said the jihadist bombers targeted a Russian airliner as a slap on the face of President Vladmir Putin for sending his forces to Syria to try and defeat the ISIS.
A former Special Branch officer warned that the success of the attack could inspire these jihadis to target British airports next, according to the Sunday Express.
Former Special Branch detective Chris Hobbs said British-born militants who have learned bomb-making skills while fighting in Syria could slip under the radar and return to Britain.
"There is a growing concern that these individuals will use their newly learnt skills to try to down an airliner here," he said, adding that "airport security here in the U.K. is very good but it can never be 100 percent."
Hobbs said the Sinai militants must have smuggled the bomb into Sharm El Sheikh airport in Egypt, with an airport worker then placing the device in the hold of the Russian passenger jet. "If that is what happened it would have needed a degree of planning," Hobbs said.
"It would be possible to hide a device inside a vehicle and then retrieve the device when the rogue employee is airside. Then it could be passed on to a security-checked passenger who could carry it on to an aircraft before becoming a martyr or possibly even placed into an unsuspecting passenger's hold baggage if that rogue employee is involved in baggage handling," he said.
Meanwhile, Putin was reported to be preparing for an all-out war against ISIS and other Islamist enemies in Syria in retaliation for the downing of the Russian jet over Egypt, the Express reported.
Investigators working on the black box said they heard a noise at the end of the voice recording, clearly suggesting an explosion aboard the aircraft before it crashed.
Defense and security experts said the mass slaughter of Russian citizens by the jihadis could escalate the war in Syria, where Putin's warplanes have been blasting targets for over a month now.
The experts said an ISIS involvement in the tragedy would "only harden Russian resolve that they need to do something stronger."