Westerners fighting with the Islamic State (IS) militant group are more violent towards prisoners than most local guards, ex-captives say.

French journalist Nicolas Henin was held hostage by IS for 10 months after being captured in Syria in 2013.

"This mad enterprise of hostage taking was mostly [a] kind of revenge of Westerners against westerners ... we were almost two dozen Western hostages held by mostly Western captors," Henin told Lateline.

Mohammed Emwazi, known as Jihadi John, was killed in a drone strike last year. ( Reuters: SITE Intel Group )

"The Middle East and Syria was mostly just a background to this story. It can sound weird … but we … were sometimes protected by local Syrian members of IS against the violence of foreigners.

"For the locals, their jihad, their holy war, had a much more local agenda.

"The Westerners joined IS and wanted to fight … because they hate everything the West represents."

Danish journalist and author Puk Damsgaard has written a book on torture survivor Daniel Rye — who was imprisoned at the same time as Henin and shared his cell — and said her subject had a similar account.

"What Daniel was explaining to me was that there was a clear difference between the local guards around him and the foreign guards," she said.

"The foreign guards … were among the most violent and I think some of the things that motivated them was clearly what they grew up [with] in back in England or back in France … and what they have seen on the international stage — political reasons rather than necessarily religious.

"It's almost like they become high off the war and the situation they suddenly live in … they had fun humiliating their prisoners, and they had fun doing the same things that American prisons have done to Muslim prisoners."

Nicolas Henin was reunited with his family in France in 2014 after being held captive in Syria for 10 months. ( AFP: Kenzo Tribouillard )

First month of captivity the hardest, author says

Rye was a Danish photographer on his first solo assignment when he was captured by IS in Syria in early 2013.

Daniel Rye, pictured in 2016, attempted suicide while being held hostage. ( AFP: Valerie Macon )

He was held hostage for 13 months. His captors included the infamous Brit known as Jihadi John.

Damsgaard said the month in captivity was the hardest for Rye and that he had tried to commit suicide, but had been saved by his guards.

"You are in shock, you don't know how to handle the new situation, you don't know what's going on," she said.

"It was also the first three weeks … that were the hardest on Daniel mentally and physically. Because he suffered lots of beatings, lots of torture, interrogations … and he actually sat alone, he had no-one to talk to.

"Later on in the captivity, he started to meet other people from other parts of the world and started to have friends who tried to support him … they start to have routines."

She said the hostages started to practise yoga together. Rye, a former elite gymnast, taught his fellow captives gymnastic routines.

Puk Damsgaard was also travelling in Syria at the time Nicolas Henin and Daniel Rye were kidnapped. ( Lateline )

Damsgaard, who was also travelling in Syria in 2012 and 2013, said journalists were caught off guard by the rise of Islamic State.

"In hindsight, it's very easy now to see what was going on, but at that time it was quite difficult to grasp the changes," she said.

"Definitely the environment towards journalists and also aid workers changed. Journalists were not necessarily seen as something positive anymore.

"So many people, whether you were young and new in the field or whether you had many, many years of experience, got kidnapped or got in trouble."

Political, not military solution needed: Henin

Henin, who has written a book on the West's treatment of IS, said the only way to defeat IS was to keep local populations in Iraq and Syria on the West's side.

"When [IS] acts in Syria or Iraq, it is much more like a guerilla movement … it's acting as a player in a very complex civil war," he said.

"[IS] are more like the symptoms of the disease than the disease itself. They developed very much because of the massacres going on in Syria … and because of the ongoing crisis.

"It's a mistake to just focus on this terror organisation. Of course, we have to tackle it … but if we don't destroy or erase the conditions that made it appear and flourish, then, another similar organisation could just pop up."

Residents help an injured man in a site hit by what activists said were airstrikes carried out by the Russian air force. ( Reuters: Khalil Ashawi )

While he said some military intervention was needed, it risked turning civilians against the West.

"What we want is to have the local population in Syria and Iraq on our side, sharing our views and siding with us," he said.

"By bombing them … we have to keep in mind that we may push them into the other side. That this is what would be our total failure."