Tens of thousands of documents containing the names, addresses, phone numbers and family contacts of jihadists who joined the Islamic State group (IS) have been given to the UK's Sky News, the broadcaster said.
Sky reported that a disillusioned former member had handed over the documents on a memory stick that had been stolen from the head of the group's internal security police.
The documents are forms that IS recruits had to fill out in order to be accepted into the organisation, and contain information on nationals from 51 countries, the broadcaster reported.
"Sky News has informed the authorities about the haul," the news channel wrote on its website. No comment was immediately available from Britain's interior or foreign ministries.
Some of the documents reportedly contain the information of previously unknown jihadists in northern Europe, the United States and Canada, as well as North Africa and the Middle East, it said.
Copies of the documents broadcast by Sky News showed that recruits would have to answer 23 questions including on their blood type, mother's maiden name, "level of sharia understanding" and previous experience.
|Hamed claimed the group had given up on its headquarters in the Syrian city of Raqqa and was moving into the desert, and that former soldiers from the Iraqi Baath party had taken over.|
Some of the names in the documents are of fighters who have been already identified, such as Abdel-Majed Abdel Bary, a former rapper from west London who once posted an image of himself on Twitter holding a severed head.
The documents were obtained from a man who uses the name Abu Hamed, a former Free Syrian Army member who joined IS.
He stole the memory stick of documents and handed them over in Turkey to a journalist, explaining that he left because "Islamic rules had collapsed inside the group".
Hamed claimed the group had given up on its headquarters in the Syrian city of Raqqa and was moving into the desert, and that former soldiers from the Iraqi Baath party had taken over.
There have been previous leaks of documents from IS, which have shown the group to be extremely bureaucratic, with rules covering every aspect of life.
But if verified the cache of members' identities would be the most significant leak so far relating to the group, which brutally carved out regions of control in Iraq and civil war-torn Syria before expanding to North Africa and further around the world.
Agencies contributed to this report