The US says the group is plotting, amid the civil war, to attack the west, while Islamist groups deny it even exists. What is it and what is it up to?

In Idlib province, they are known as “the strangers with the horses”. Among the senior ranks of Jabhat al-Nusra, they are referred to as “our friends”. In Europe and the US, the small band of jihadis is known by the contentious name “Khorasan” and blamed for hatching plots to attack the west.

All seem to agree on one thing: just what the highly secretive group is up to in northern Syria remains one of the civil war’s enduring mysteries. This week, the leader of Jabhat al-Nusra claimed there was no such group as Khorasan and said he had been directed by al-Qaida’s central leadership to concentrate his group’s energies on Syria.

Abu Mohamed al-Jolani’s remarks, in an interview with al-Jazeera, were the first time that al-Nusra – a jihadi organisation with links to al-Qaida and a formidable player in the Syrian war – had addressed the issue of Khorasan, which the US accuses of collaborating with al-Nusra to target western interests outside of Syria.

The remarks were immediately rejected by western officials and residents of Idlib. Two senior Islamists with close links to al-Nusra have also outlined to the Guardian in recent weeks their understanding of Khorasan’s intent and its close ties to homegrown jihadi groups.

“Until recently they wanted nothing to do with the Syrian war,” said one ranking official. “They only wanted to use Syria as a stadium for whatever they were up to elsewhere.



“But that’s different now. In the attack on Idlib city they played a direct role. They co-ordinated most of the dangerous attacks. Without them, Idlib would not have fallen.”

Syria not a launching pad for attacks on west says al-Nusra chief in TV interview Read more

The claim that Khorasan had played a direct role in helping jihadi and mainstream elements of the Syrian opposition seize a major city marks the first time that any official has been prepared to acknowledge working alongside the group. “They are a very big secret, you know,” the official said. “They work directly for [al-Qaida leader Ayman] al-Zawahiri.”

Until recently, all residents and jihadis interviewed by the Guardian had painted a picture of a remote and impenetrable outfit that kept entirely to itself and whose members regularly moved to avoid US air strikes.



On the first night of a US-led air campaign, ostensibly to attack the Islamic State group last September, three bases for Jabhat al-Nusra and a second jihadi group, Ahrar al-Sham, were bombed in the opening salvoes.



The attacks killed more than 70 militants and Washington claimed to have struck cells of leaders who had been seconded to Khorasan and tasked with scoping for targets outside of Syria.



Both groups quickly denied any connection to Khorasan, and vowed vengeance against the US. Al-Nusra officials claimed they had not heard of Khorasan, leading the US to claim it had been monitoring its growth for more than two years as the opposition landscape had splintered and radicalised in parts of Syria’s north. Two local residents say the people they referred to as “the strangers with horses” first moved into the Idlib countryside early in 2013.



“They were from all the places that end in ‘stans’,” said one man. “Uzbekistan, Afghanistan, Tajikistan, places like that. “They dressed like Osama bin Laden’s mujahideen and they slept in the forests with their horses next to them. Big, beautiful stallions. They wanted nothing to do with us, or any of the opposition groups.”



A second resident said that the group was known locally as Khorasan by the end of 2013. “Although it became difficult to know who was directly with them and who was with [al-Nusra]. They started to become similar.



“But until the Americans bombed them, we didn’t know what they were up to. And we still don’t.”



One senior jihadi confirmed to the Guardian that the group’s leader was Muhsin al-Fadhli, a veteran of al-Qaida who had travelled to Syria at the beginning of 2013 along with a small number of other members of Ayman al-Zawahiri’s inner circle.



The US government claims that al-Fadhli, a Kuwaiti, was one of the few Bin Laden confidantes who knew about the 9/11 attacks ahead of them being carried out.



The Pentagon claimed to have killed al-Fadhli during an air strike on 22 September, but later said he had survived the strike. A French jihadi, David Drugeon, was believed to have been badly wounded.



Critics of the US decision to fight Isis in Syria and Iraq point to Khorasan’s complete lack of profile before the air strikes and claim its emergence was a convenient pretext to justify intervention.



Local officials, though, say the group was gathering strength throughout 2014. One official said Khorasan leaders now remained on the move to avoid air strikes. “Everywhere they go, the Americans are looking for them,” he said. “Their houses get blown up all the time.



“I don’t doubt that they are planning something outside Syria. But it is impossible to know. There are no Syrians working directly for them. Only big men from al-Qaida. To be honest, when they worked with Nusra in Idlib, it was the first time.”



In denying Khorasan’s existence, or being linked to any plan to attack targets outside of Syria, Jolani appeared to be positioning al-Nusra as a more palatable jihadi current, distinct from the unchecked savagery of Isis.



However, western officials say Khorasan remain near the top of the list of potential threats to the US, the UK and Europe, with no sign that any order from Zawahiri had eased the threat.

“They are more prominent than before,” said the second Nusra-aligned leader. “The one thing that hasn’t changed though is that no one wants to speak about them.”