Mumbai- As investigations into Thursday's Pune blast progress, agencies are worried about two youths from Thane (near Mumbai) who are reported to have left for Iraq to fight along ISIS about a year ago, Indian media quoting officials reported on Sunday. These two boys are part of the 18 Indians learnt to be fighting in Iraq and Syria and are being tracked by intelligence agencies. Sources within the security establishment say most of these 18 hail from south India. Some of those who have been identified belong to Maharashtra, Karnataka and Tamil Nadu. It is not known whether any of them has returned but such exodus from south India has become a cause for worry for the agencies. ISIS chief Abubakr Al-Baghdadi, who recently declared himself as the Caliph of Islamic State (as the group is now known to be in pursuit of establishing a Caliphate in West Asia), has asked Indian Muslims to wage war against the nation in an audio message. "Many of these men who joined the war through Singapore have been identified — two are from Thane, one from Bangalore and another from Chennai. There are others who come from interiors of Karnataka and Andhra Pradesh. Surprisingly, none of them is from north India even though a bunch of UP youths owing allegiance to Indian Mujahideen has been fighting in Afghanistan alongside the Taliban and al-Qaida," said an officer from the security establishment. As reported in an Indian media, of the 18 aspiring jihadis on the radar, six men have already left Iraq, disenchanted by the way they were treated by terror groups, and are now reported to be in gulf nations. None of the 18 belongs to any particular group but all have been individually radicalized through internet literature and videos. Indian agencies, however, say there may be many more in Iraq fighting alongside ISIS that they are not aware of. "Our difficulty is that a steady stream of people from our country goes to the Gulf and West Asia as laborers. Sorting out those who have gone there for jihad is a huge task. It is for European nations and the US to sort out the suspects as exodus from a rich nation to a poor one has the potential to arouse suspicion," said the officer. The major concern for Indian agencies is that sooner or later these battle-hardened fighters will come back to India. "With no war to fight and no purpose to motivate them, they will try to create one here. Given that they could have their contacts with global terror networks alive, they could precipitate real problems for the country," said the officer. Western nations, which suspect around 2,000 youths from Europe and the US to be fighting in West Asia, have already woken up to this threat in their own countries. With India already in ISIS crosshairs, agencies are working overtime to track these elements.