A child sits in a truck full of furniture as a family collect belongings after months of shelling by regime forces of a rebel-held area north of Damascus

Members of the Kurdish People's Protection Units are put through their paces at a training camp

'It was either fight with ISIS or they will kill me", says Abu Omer. So he complied with orders and assumed a role in the frontline for ISIS in the strategically important city of Deir Ez-Zor, fighting there from July until late December, 2014.

"It's difficult for anyone to leave," explains Abu Omer - which is not his real name to protect his identity. "People have no money and they have families" to take with them. There are also several checkpoints.

Omer is - for now - in hiding in the city of Urfa, on the Turkish border with Syria, having escaped from Deir Ez-Zor and ISIS. He's a former Group Leader with the 'Al Qadisiya' brigade of the Free Syrian Army; his unit was defeated by ISIS in Deir Ez-Zor, during the militant group's spectacular takeover of large swathes of land in Eastern Syria and Western Iraq last June and July.

Captured Syrian fighters like Omer, who are there involuntarily, are not considered fully supportive of the Caliphate, and are therefore never far up the command structure or trusted with leading military offensives.

Omer, like other Syrians who joined to revolution against the Assad regime in late 2011, wait for their orders at the frontline - they're told when to target the enemy, be it local Jihadist groups with a similar ideology, like Al Qaeda-linked Jabhat al Nusra, or the Syrian army of Assad. Nor are they often ordered to mete out the medieval punishments like beheadings or crucifixions, that have become part of daily life for Muslims living under ISIS control.

Omer reckons that up to 70pc of the ISIS fighters in Deir Ez-Zor are foreign - including about 40 Irish. His estimates reinforces information from several sources, including the US National Counter-Terrorism Centre. "All of the countries of the world have fighters inside Syrian fighting with ISIS," he says. "The most European fighters were from France, there were some from the UK, and there were Irish, but the most was French.

"There was Chechen, Libyan, Moroccan, Tunisian, Egyptian, and Saudi Arabian, some also from America.

"ISIS depends on Chechens the most," for their military prowess and dogged violent nature, "If ISIS wants to take over any area, they send the Chechens in.

"The Irish fighters are perfect snipers; they use them sometimes with the Chechens, in any place they need snipers, they move the Irish," he adds.

"They are part of the Al Khalifa army (Caliphate army), and fought in Kobane," before the Kurdish Peshmerga forces with the help of coalition forces, defeated them.

While Abu Omer says there are around 40 Irish fighters in Deir ez Zor, the Department of Justice's official figure is that 30 Irish fighters have left here to fight in Syria and Iraq. Sources in the US State Department, however, say this number is closer to 70 in total.

Of the Irish, Abu Omer came across, one was known as 'Abu Omer al-Irlandi', another, 'Abu Yazid al-Irlandi'. They work alongside British jihadists, "you see them together" says Omer.

Foreign fighters from Europe have the most virulent ideology he also claims. They are the most dogmatic when it comes to ISIS ideology.

"Sometimes the Saudi or other Arabic fighters might forgive you if you are caught smoking or caught breaking the rules," but not the Europeans.

The Europeans are "the devil" inside Syria. "They cut the heads". In one incident, a French jihadist known as 'Abu Ali-al Franci' "cut three heads inside Deir ez-Zor centre," claims Abu Omer. Although he did not provide photographic evidence of this, Abu Omer's character and identity was corroborated by sources from Deir ez-Zor, and within the FSA brigade that he once held a senior position in.

"Another example: in a village in the Deir ez-Zor countryside, the Europeans killed around 3,000 people in the village, using French fighters," he says.

When they (ISIS) decide someone is 'kuffar' - a non-believer, or someone that has rejected Islam- "they use European fighters to cut heads, to kill people".

According to Omer, and other members of the FSA, the foreign fighters operating under the IS banner, believe they "are, the Islamic State", and not fighters in a foreign land, but the beginning and creators of the new Islamic caliphate; the rising Caliphate. The fact that they are not born in, nor have any personal ties with the land that they have so savagely overrun is irrelevant, as is the fact that some are not born in to Muslim families and converted only recently.

Restrictions on women are akin to those in Taliban-controlled areas of Pakistan and Afghanistan; their faces are completely covered, they wear only black shoes and "have been punished for wearing other colours". "I didn't see any women killed by Daash (the local Arabic name for Isis). Girls are forced to get married to European and other fighters. Women aren't allowed learn or go to school; they have to stay inside the house. She can't go outside without her father, brother or husband, nor gather together with other women unless very necessary.

"I've known of British women who have joined Daash, but never heard of any Irish women," he says when asked whether he knew of Irish female jihadists.

ISIS' success in grabbing the attention of western leaders and public at large is very much due to the publicised murders of several journalists, aid workers and more recently Jordanian pilot, Moaz al-Kasasbeh. All deaths appear to be carried out by one of ISIS' most barbaric operatives, nicknamed Jihadi John, who's rumoured in a previous life to have once been a rap singer from London.

"That's what I heard about him. His security is very high - like Abu Omar al-Baghdadi" - ISIS' founder from Baghdad, Iraq.

"They move him place to place; they're afraid he will be tracked by satellite".

"They use him because he's a British man to kill the Europeans and westerners".

Last October, in Turkey, a foiled kidnap attempt of Syrian army leader Abu Issa by ISIS illustrated both the presence and willingness to operate inside Turkey's borders, as well as the increased number of Turkish security forces.

Yet the onus is not just on Turkey to stem the tide of extremists crossing the border, but on western societies in stemming the tide of radical young men and women from leaving their respective countries, and deprogramming them of their radical intentions, lest they remain in their home country and act out ISIS-inspired attacks on home soil.

"They can attack Europe any time they want; they have members inside Europe, inside America, inside Britain, they're just awaiting a decision from al-Baghdadi.

"They focus on America, Britain, France and Denmark, because of the cartoons about Mohammad, warns Omer.

Shona Murray presents Newstalk's World in Motion show, Sundays, 8am to 9am

Sunday Independent