UK prisons are making arrangements for a possible influx of Islamic State fighters, the Justice Secretary has said.
David Gauke said a "lot of work" is being done as authorities take action to ensure they are prepared in case British militants attempt to return to the country.
The Government estimated that more than 850 UK-linked individuals "of national security concern" travelled to engage with the Syrian conflict.
More than 15% of those who travelled have been killed in fighting, while just under half have already returned.
A significant proportion of those who have come back are assessed as no longer being of national security concern.
Police have indicated that, of those who made the journey and remain in the region, around 100 could in theory seek to re-enter the UK.
In an interview with the Evening Standard, Mr Gauke declined to say how many he expected to return.
He said: "There is a likelihood that we are going to see people returning from the Middle East in the months ahead and many of them are going to become our problem within the prison system.
"We need to make sure that there's the proper approach to them.
"This is an issue that is going to be very significant for the criminal justice system as a whole and the prison system and is one of the big challenges that we have to face."
Last year the Ministry of Justice launched three specialist units to hold up to 28 prisoners after a review concluded Islamist extremism was a growing problem in jails.
At the end of December there were 224 individuals in custody in Britain after being charged with or convicted of terrorism-related offences, an increase of 24% compared with a year earlier.
Mr Gauke also warned that society must take action to prevent children being brought up "in an environment that leads them towards a belief in a death cult".
Last month Mark Rowley, the outgoing police counter-terrorism chief, questioned whether there should be "more parity" between measures taken to protect children from paedophile and terrorist parents.
Since the start of the Syria conflict around 100 children have been safeguarded through the family courts.