The names of three of the Paris attackers appear in files leaked from the Islamic State militant group, according to German media reports.
The three are believed to have carried out the worst attack, at the Bataclan theatre, where 90 people died.
The IS files, obtained by German, UK and Syrian opposition media, are said to identify thousands of jihadist recruits from at least 40 countries.
German officials have said the files can be assumed to be genuine.
Roughly 22,000 fighters are reportedly identified by the documents, with one file for each recruit listing a name, address and other information. However, many of the names given may be duplicates.
Among them are Samy Amimour, Foued Mohamed-Aggad and Omar Ismail Mostefai, the three men who attacked the Bataclan during a concert by Eagles of Death Metal, killing 90.
The documents have been obtained by German public broadcasters WDR and NDR, and the daily Sueddeutsche Zeitung.
WDR said the files indicate that the three men entered IS territory in 2013 and 2014.
Germany's Interior Minister Thomas de Maiziere earlier said the information contained in the files could help to prosecute IS fighters, and help prevent future recruitment.
Files were first published online (documents in Arabic) by Zaman Al-Wasl, a Qatari-based Syrian news website.
Sixteen Britons reportedly appear in the files, including Junaid Hussain and Reyaad Khan, who were killed in September in Syria by an RAF drone strike.
Two others listed, Kerim Marc B and Abdelkarim B, are currently on trial separately in Germany, while another two Germans on the list, Farid Saal Yassin Oussaiffi, have appeared in IS videos.
Dutch media identified Abu Jihad al-Hollandi from the documents as Amsterdam teenager Achraf Bouamran, who was killed in a US air strike on the Syrian IS stronghold of Raqqa in January 2015. His file reads: "Born 1997. Moroccan origin. Wants to be a fighter."
Counter-terrorism police in Germany are studying the documents.
"The German Federal Bureau of Investigation acts on the assumption that the documents are authentic," de Maiziere said.
His counterpart in the UK, Home Secretary Theresa May, said she could not comment on "specific national security matters".
IS "poses a severe threat... it is important for us to work together to counter this threat", she said.
French Interior Minister Bernard Cazeneuve said: "We are extremely interested in information which would allow us to ... neutralise terrorists, but such information has to be authenticated."
Sky News said the documents came from a man called Abu Hamed, an IS fighter who said he had become disillusioned with the group's leadership and stolen a memory stick from the head of the IS internal security force before handing it over in Turkey.
Stefan Kornelius, foreign editor of Germany's Sueddeutsche Zeitung newspaper, told the BBC the paper had obtained the documents from a "trusted source".
"It gives some proof on the state of Isis [IS] right now, since many of those members and those being close to the terrorist group are trying to make money, quite honestly, because obviously the Isis is in a desperate financial state," he said.
Are the documents genuine? Analysis by BBC Monitoring jihadist media expert
Some analysts have raised questions about the authenticity of the documents, noting inconsistencies in language and other oddities in the recruitment questionnaires such as:
- The old name for IS - Islamic State in Iraq and the Levant (Isil) - is rendered in two slightly different ways on the documents
- An unusual logo is used at the bottom saying "Islamic State is here to stay"
- The questionnaire has a section for recording when and where a fighter was "killed" rather than "martyred" - jihadists' preferred terminology
But none of that is conclusive. The documents were clearly not intended for public consumption, so those who drafted the questionnaire may not have paid as much attention to detail as for public documents.
And they should be compared not with IS documents of today, but of around two years ago, when they appear to originate - before the group's rapid land grab across northern Iraq and Syria, when its bureaucracy and administrative capabilities were less well developed.