Copenhagen Police have been secretly investigating controversial preacher Abu Ahmed, his Quba mosque in Amager and the charitable organisation Hjælp4Syrien. The investigation is centred on allegations that Ahmed and his associates have encouraged people to travel to Syria to take part in the civil war there and that monies collected under the guise of charitable donations are being used to fund terrorism.

Jens Møller, head of the Copenhagen Police's violent crime division, confirmed that they have been investigating a number of separate cases since March, including posts on the Quba mosque’s Facebook page via the educational branch operated by Ahmed, Islamisk Undervisning, that seek financial support for the al-Nusra Front in Syria.

"We can confirm that there is an investigation in progress based on new information, including the support of al-Nusra Front,” Møller told Jyllands-Posten newspaper. “We cannot comment further.”

The al-Nusra Front, according to Western intelligence agencies, was formed by al-Qaeda in Iraq. Published reports claim that the group is in regular contact with Ayman al-Zawahiri, the recognised global head of al-Qaeda and successor to Osama bin Laden.

Fears are increasing that the more than 6,000 foreign fighters who have poured into Syria from around the world in recent months pose a significant new terror threat to the West. Intelligence reports say that camps are being set up to give the foreign fighters combat training.

Ahmed is a well-known figure in Islamist circles in Denmark. Besides the Quba mosque, he has taught at several other places in Copenhagen. He attracted the attention of domestic intelligence agency PET for having provided spiritual guidance to two young people involved in planned large-scale Copenhagen terrorism cases.

Allegations that Ahmed and members of his mosque had financially supported a Danish resident who was killed while fighting for Syrian rebels were published by Jyllands-Posten last spring. Calls for support for al-Nusra have been posted on the mosque’s Facebook page and Ahmed issued a statement of support for former Danish Guantanamo Bay prisoner Slimane Hadj Abderrahmane, who was reportedly killed in Syria sometime in February, four days before the death was reported by the media. As recently as last Thursday, the mosque’s Facebook page reported that Danish resident Abu Omar Altunes was killed in the fighting in Syria and asked for support for the dead man’s family.

The latest numbers show that at least 65 people have travelled from Denmark to fight in Syria and, including Altunes, six of them have now died. Copenhagen police and PET are concerned that those who make the trip to Syria become completely radicalised and the skills that they learn in the construction of bombs and the use of other weapons make them a risk to Denmark when they return. PET says that most of those travelling to take part in the combat come in contact with al-Qaeda.

Police are trying to trace the path of funds collected by Hjælp4Syrien, but admit it will be difficult to prove that contributions are supporting terrorism.

"We have to find out who is really behind the collection and determine whether the money has gone to activities that can be equated with terrorism,” said Møller. “If the case goes to court, it will ultimately be up to a judge to determine whether we have provided ample proof.”

Among the problems that the police have in pursuing the case is that al-Nusra and other groups that may be receiving funds from Hjælp4Syrien are not currently on the EU terrorist watch list.

PET has announced plans to prosecute Danes who get involved in the war in Syria, but acknowledge that it will be tough to prove when or if someone had been engaged in acts of war for a specific organisation at a specific time. Reports coming out of Syria are not considered particularly reliable.

PET has asked the tax authority Skat to investigate who is funding the Syrian trips and have asked local authorities to see if those who are heading to the war zone are receiving any social benefits from Denmark.

Abu Ahmed has declined to comment on the allegations.