"Depending on which expert you speak to, there have been about 300 and 500 British citizens who have gone to Iraq and Syria. Many of them fight for ISIS; many of them don't come back. It just takes one person to continue that sort of behavior in this country for it to be a big problem," Khan told ITN.
His comments came after British Islamists in Syria released a recruitment video to help enlist followers. Khan said ISIS's attempts to garner support can be countered by an effort to help British citizens resist the message of radical Islamists.
"We should be encouraging our citizens to be resilient, make sure they know the real version of Islam so when the charismatic preacher of hate comes along, they can be resilient to that message. Make sure we work more closely with those who control the borders in Turkey, Iraq, and Syria so they know these people are going there for bad reasons and to turn them back Make sure we spot them when they come back," he said.
He also noted that the best way to help with the deteriorating situation in Syria refrain from joining the fight.
"We've got to explain to people that the idea you are being a help by jumping on a plane and going to Syria and Iraq is nonsense. If you want to the people who suffered as a consequence of the civil war, you can get involved in charities, you can give money and there are other things you can do."