France's top anti-terrorist judge has warned that Iraq is a black hole which has helped to radicalise some young Muslims and drawn them into violence.
Bruguiere: Has tracked terror suspects for more than two decades
In an interview with the BBC, Jean-Louis Bruguiere says some Muslims are receiving training in Iraq before returning to Europe to carry out jihad.
He also warns that the terror threat facing Europe remains very high.
Combating Islamist terrorist cells is becoming harder as they are fragmenting in unpredictable ways, he says.
Judge Bruguiere is one of Europe's most experienced anti-terrorism investigators, who has specialised in tracking Islamist groups since the 1980s.
In his interview with the Today programme, he says he is pessimistic about the immediate future - saying the terror threat in Europe and the rest of the world remains very high.
He says Iraq has helped to draw some young Muslims into violence.
"It's quite a black hole sucking up all the elements located in Europe, and pushing them to leave Europe and go to Iraq," Mr Bruguiere said.
"Some of them come back to Europe with the need and the intention of committing jihad... in their home country in England, France, Spain, other country in Europe.
"Some of them have training for non-conventional weapons such as chemical and biological weapons and that were quite new in 2002, 2003."
The BBC's security correspondent Gordon Corera says Judge Brugiere's concern over Iraq is widely shared, even by the CIA, according to leaked reports.
Afghanistan, Bosnia and Chechnya in the 1990s were magnets for young jihadists and if Iraq is now playing the same role then it may well be Europe that feels the after affects as well as countries in the Middle East, our correspondent adds.
There are fears Iraq violence could have a knock on effect
According to our correspondent, French officials are conscious that the violence of Algeria through the 1990s helped generate a reservoir of highly radicalised individuals who were well versed in terrorist techniques and who wanted to attack France.
French officials now fear that Iraq could play the same role in the next decade and that the battle to track these individuals and prevent more being drawn to their cause will take years.
Judge Bruguiere warns that combating the threat is becoming inceasingly difficult.
He likens terrorist cells to a virus which continually mutates - making co-operation on intelligence-gathering more important than ever.
Judge Bruguiere says one of the most worrying developments is evidence that some cells are now acquiring non-conventional weapons, with French intelligence foiling a would-be chemical attack in 2002.
Concern about a possible terror attack has increased in France in recent weeks, not least with the rounding up of an alleged terror cell in late September who were said to have been planning attacks in Paris.
A top counter-terrorist co-ordinator in the Interior Ministry told the French newspaper Liberation that the French intelligence services were particularly worried about attacks by French Algerians following a communiqué on the internet from an Algerian militant group threatening France as "enemy number one".