Fourteen people have been arrested over suspicion of preparing fake passports and other documents for the Islamic State group militants, Russia’s Federal Security Service (FSB) reportedly said Thursday. The people, who were part of an international organized crime network, were taken into custody during a joint operation by the FSB and Interior Ministry.

The suspects were reportedly forging passports for extremists to travel to Syria and also for those returning to Russia to carry out terrorist attacks.

“After collecting the needed base of evidence in the criminal case, ... a complex of operative military and investigation operations were carried out in the capital’s region to suppress the activities of the group revealed by detaining 14 of its members ‘red-handed,’” the FSB said in a statement, according to Sputnik News

The criminal group was forging documents for those “illegally heading to Syria to take part in military actions on the side of Islamic State, and also for the militants sent on a mission to Russia by ISIS leaders to conduct terrorist and extremist activities, as well as illegal migrants,” the FSB added.

The Russian security agency reportedly said that the suspects were arrested after authorities found sufficient evidence, including a vast stockpile of forged documents, forms, stamps, special equipment for fake papers’ production, during search operations.

Last month, the Russian tourism agency cautioned that ISIS had plans to take Russian tourists hostage in Turkey and possibly transport them to Syria.

The Russian government has been concerned about the country being a potential recruiting ground for Islamic militants because of its proximity to the Middle East.

Last December, the Russian Interior Ministry reportedly said that up to 2,000 Russian nationals were believed to have been linked to ISIS-related military activities.