Iraq's top Shi'ite cleric Grand Ayatollah Ali al-Sistani said on Friday regional states were not doing enough to stop the flow of militants into Iraq, and warned that the fighters would return one day to threaten their home countries.
The Islamic State group has attracted Sunni Muslim fighters from across the world to its self-declared caliphate in parts of Syria and Iraq. Large numbers have fought on the front line or carried out suicide bombing missions.
Sistani's representative Sheikh Abdulmehdi al-Karbalai said the prominent role of foreign fighters was a sign of international negligence.
"The continuation of this policy of indifference and the intentional or non-intentional ignoring of the flow of these members to Iraq will increase the peril of these gangs to the country and entire region," Karbalai said in a Friday sermon.
"It will pose a real threat to their home countries. It is possible that they will return to them in the future to form terrorist cells that will participate in disturbing the safety and security of those countries," he added.
A growing number of attacks in the Middle East have been claimed in the name of Islamic State supporters, particularly in North Africa and Gulf Arab countries.
"The neighboring and international countries that these terrorists come from are invited to take serious measures to prevent the enlisting of new members to this terrorist organization," Karbalai said.
