Hundreds of foreigners could unknowingly be fighting for President Assad following reports of a deal struck between the regime and extremist group Isis.

It is every jihadist’s worst nightmare: the prospect of fighting against the Assad regime in Syria, only to discover that you have done precisely what the Syrian president wants.

Hundreds of foreign fighters are falling prey to a suspected pact between President Assad and the extremist group the Islamic State of Iraq and al-Sham (Isis).

On the surface, the two parties are bitter enemies. On the one hand, Isis, a former affiliate of al-Qaeda, which wants to create an Islamic state which disregards the border of Iraq and Syria alike.

On the other, President Assad – a leader who tries to justify war against his own people by citing the danger posed by Isis and other extremist groups.

Yet could both now really be in some sort of unholy alliance? Yes, says the Western-backed Syrian National Coalition, which claims Isis and regime forces have become “intimately intertwined”.

A recently released memo suggests that while the two sides differ in motives, they are bound by a common goal: “to destroy moderate opposition forces and establish control of as much of Syria as possible.”

A Faustian pact

It cites evidence from across the country, including regions such as Raqqa, Jarablus and Al-Danna, that Isis headquarters escaped unscathed in the midst of heavy shelling from Assad’s forces.

In return for this favour, the memo suggests that Isis – which already controls much of north eastern Syria – has chosen not to attempt to take areas such as Dier Ezzor, Aleppo City or Jisr Al Shughour, which are under the control of the regime.

There are also reports of trade deals on oil and gas struck between Isis and the Syrian government.

‘Working hand in glove’

David Butter, a leading expert on Syria and an associate fellow at think-tank Chatham House, told Channel 4 News that the links between Isis and Syrian intelligence date back to the aftermath of the Iraq war of 2003.

“The leaders Isis have already worked hand in glove with Syrian intelligence, whether supplying them with weapons or supplying money flowing from their racketeering activities around Mosul.”

He added: “Intelligence officers will have almost certainly forged links during that time and there has almost certainly been some degree of regime manipulation. To what extent one is actually controlling the other is more difficult.”

And the UK government is certainly not ruling out a partnership, either. A spokeswoman for the Foreign Office told Channel 4 News that while it could not verify the claim directly, there was “anecdotal evidence that adds up”.

“Assad has a long history of supporting terrorist groups and activity in the region. There have been pictures of Isis flags on buildings that have escaped shelling and reports of supposed collusion on oil and gas deals. It is not definitive – but certainly lends credibility to the suggestion.”

Destination unknown

But could there be an even darker motivation to the alliance? It was reported this week that Isis is funneling foreign volunteers from Syria through Turkey and into Iraq. It is a move aimed at bringing the Iraq to the brink of civil war.

This raises the even more heartbreaking possibility of foreigners in Syria believing they are there to overthrow Assad, only to find themselves embroiled in something far darker.

British security services are increasingly desperate to find ways of dissuading a wave of Britons from going to fight in Syria.

“Go to Syria and end up helping Assad,” could be their most powerful message.