The suspected ringleader of the Paris attacks, Abdelhamid Abaaoud, was among those killed in a French police raid on Wednesday, prosecutors say.
They confirmed Abaaoud had died when anti-terror police stormed a flat in the Paris suburb of Saint Denis.
His body was found riddled with bullets and shrapnel in the apartment.
Interior Minister Bernard Cazeneuve said he had received intelligence that Abaaoud passed through Greece on his return from Syria.
It is unclear whether he had concealed himself among thousands of migrants arriving in Greece before heading for other EU nations.
Confirming the Islamic State (IS) militant left for Syria last year, Mr Cazeneuve said no EU states had signalled his return.
The minister also implicated Abaaoud in four out of six attacks foiled in France since this spring.
The Belgian national, 28, was identified from his fingerprints.
Friday’s gun and suicide bomb attacks in the French capital left 129 people dead and hundreds injured.
Eight people were arrested and at least two killed in the raid on the property in Saint Denis. Heavily armed police stormed the building after a tip-off that Abaaoud was in Paris.
A woman at the flat – reported in French media to be Abaaoud’s cousin – died during the raid after activating a suicide vest.
The prosecutor’s office said it was still unclear whether Abaaoud had blown himself up or not.
Mr Cazeneuve told reporters that a non-EU state had alerted France on Monday that Abaaoud had been in Greece.
“Everyone must understand it is urgent that Europe wakes up, organises itself and defends itself against the terrorist threat,” he said.
2013: Said to have first visited Syria, joining the Islamic State group before slipping back to his home country, Belgium
2014: Back in Syria where he became one of the faces of IS propaganda
16 November 2015: A foreign intelligence service alerts France that he is back in Europe, having passed through Greece
18 November 2015: Killed in police raid on Paris suburb of Saint Denis
Investigators are still looking for another suspect, Salah Abdeslam, who is believed to have travelled to Belgium after the attacks on Friday night.
The BBC’s Hugh Schofield in Paris says the identification of Abaaoud raises serious questions for security services.
He was high on French and Belgian wanted lists and yet managed to travel from Syria to the heart of Paris without ever leaving a trace.
More on the Paris attacks
- A doctor’s story An emergency department medic describes his Friday night shift
- Rethinking strategy Time for West to review its priorities in Syria
- How vulnerable is Europe? Putting the dangers in perspective
- What happened in Paris? How events unfolded on Friday evening in the French capital
- Hollande upstages opposition French president’s tougher line on counter-terrorism
- Who were the victims? Details of some of the 129 people killed
- The fight against Islamic State Can a modern, open Western capital ever be totally secure?
- Most wanted: Alleged ringleader Profile of Abdelhamid Abaaoud
Earlier on Thursday, Belgian police raided properties linked to Salah Abdeslam , who is believed to have blown himself up outside the Stade de France stadium during Friday’s attacks.
Several raids took place in and around Brussels and one person had been detained, Belgian prosecutors said.
Meanwhile, French PM Manuel Valls warned that France could face chemical or biological attack from terror groups, as deputies voted to extend the state of emergency imposed after the attacks for another three months from 26 November.
What is Islamic State?
IS is a notoriously violent Islamist group which controls large parts of Syria and Iraq. It has declared its territory a caliphate – a state governed in accordance with Islamic law – under its leader Abu Bakr al-Baghdadi.
What does it want?
IS demands allegiance from all Muslims, rejects national borders and seeks to expand its territory. It follows its own extreme version of Sunni Islam and regards non-believers as deserving of death.
How strong is IS?
IS projects a powerful image, partly through propaganda and sheer brutality, and is the world’s richest insurgent group. It has about 30,000 fighters but is facing daily bombing by a US-led multi-national coalition, which has vowed to destroy it.
‘No timetable’ for Syria strikes vote
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