French jihadis should be allowed to return home to prevent a new wave of attacks, an anti-terror magistrate has warned.

David De Pas, French anti-terrorist judge, said 'knowing that these people are in the care of the judiciary' rather that allowing them to 'roam free' would be better for public safety.

Turkey's offensive against Kurdish militia in northeast Syria has sparked fears that some of the 12,000 jihadists, including thousands of foreigners, being held in Syrian Kurdish prisons could escape.

Between 60 and 70 French fighters are among those held with around 200 adults, including jihadists' wives, being held in total, along with some 300 children, according to Paris officials.

David De Pas, French anti-terrorist judge, said 'knowing that these people are in the care of the judiciary' is better than allowing them to 'roam free'

France has so far refused to allow adults to return home in order to make them face local justice with only a few children, mostly orphans, taken back.

Foreign Minister Jean-Yves Le Drian travelled to Iraq this week to convince Baghdad to take in and try French jihadists being held in northern Syria.

However De Pas argued that instability in the region and the 'porous nature' of the Syrian Kurdish prison camps risked triggering 'uncontrolled migration of jihadists to Europe, with the risk of attacks by very ideological people'.

The Turkish offensive, which has detracted the Kurds' attention from fighting IS, could also facilitate the 're-emergence of battle-hardened, determined terrorist groups.'

A member loyal to the Islamic State in Iraq waves an ISIL flag in Raqqa, Syria. Between 60 and 70 French fighters are among those held abroad with around 200 adults, including jihadists' wives

This in turn could spur the establishment of new jihadist networks to supply 'French citizens drawn to these groups,' he argued.

Warning of the risk of 'a new vicious circle' of radicalised young French people travelling to Syria, De Pas called on the government to demonstrate 'the political will to repatriate' the fighters.

Last month, IS chief Abu Bakr al-Baghdadi urged the group's followers to break jihadists and their family members out of prisons in Iraq and Syria.

According to Syrian Kurdish authorities, nearly 800 wives and children of foreign jihadists escaped from a camp for the displaced on the first weekend of the Turkish offensive.

At least three French women ended up in the hands of the Islamic State, according to their lawyer.

Making the case for the fighters to be brought home, De Pas pointed out that Paris had for years been successfully taking back and jailing jihadists expelled from Turkey.

'I understand that there may be nervousness but how we can we protect ourselves if we don't have our hands on them?' he asked.

The magistrate, who said he was speaking out on the issue because 'I would feel responsible if I didn't say it', also warned against the temptation of transferring jihadists to Iraq to face justice there.

'Once they had been tried and served their sentences in Iraq they would disappear under the radar', he said.

In France, by contrast, 'if in 15, 20, 30 years these people still constitute a threat on leaving prison... they will remain under the watch of the intelligence services and the justice system.'

Investigating magistrates are independent of the government, but it is extremely rare in France for them to publicly challenge policy.