- The four believed to have flown together to Istanbul via Milan in September
- It is believed they are the most members of one British family to join IS
- Wednesbury pair may have been radicalised by extremist at local mosque
Four members of the same family are suspected forming a real-life British Muslim 'band of brothers' by travelling to Syria together to join the so-called Islamic State insurgency.
Two siblings, aged 17 and 20, from Camden, north London, and their cousins, aged 19 and 22, from Wednesbury, West Midlands, are alleged to have run away from home to join the jihadists.
All four are believed to have flown together from London via Milan to Istanbul, before apparently making their way across the border into Syria, The Sunday Times reports.
Two of the men were named in the paper as Mejanul Islam, 22, and his brother Kamran, 19, brothers from the Black Country.
They and the London pair - who are not named - are said to have travelled in September, just as a U.S.-led coalition of Western and Arab states started bombing Isis positions in Syria.
Scotland Yard began investigating after the brothers from Camden were reported missing by their parents.
Mejanul and Kamran's father, Saydul Islam, a restaurant worker, told Sunday Times reporter Dipesh Ghader his sons vanished after telling him they were off to visit relatives in London.
'We've had no news at all,' the 43-year-old said. 'I don't know where they've gone. We're very worried.'
More militants: All four of the British recruits from one family are believed to have flown together from London via Milan to Istanbul, before apparently making their way across the border into Syria
It is not the first time that sets of siblings have travelled together to Syria to join the Islamist-inspired Sunni insurgency over there.
British medical student Nasser Muthana and his younger brother Aseel, from Cardiff, travelled to Syria over the summer.
Nasser is believed to have since featured in a gruesome video showing the decapitation of Syrian servicemen.
In July Zahra and Salma Halane, both 16, of Chorlton, Manchester, also ran away from home to travel to Syria where they married fighters after being radicalised online, earning them to sobriquet the 'terror twins'.
However, the case of Wednesbury's Islam brothers and their cousins from London is believed to be largest number of fighters from a single British family to travel abroad to join Islamic State.