According to a report by the Financial Times newspaper, a Syria opposition source speaking on condition of anonymity said he had “verified 100 executions” of foreign ISIL militants in the city of Raqqa.

Militants belonging to the extremist group in Raqqa have spoken of a military police created to clamp down on foreign members who do not report for duty.

The report added that dozens of houses have been raided and many militants have been arrested.

British media in October reported that five Britons, three French, two Germans and two Belgians sought to come back home, but the terror group had imprisoned them.

Researchers at the International Center for the Study of Radicalization at King's College London have found out that in total, between 30 and 50 Britons want to return but fear jail.

According to a recent report by the UN Security Council, 15,000 people have flocked to Syria and Iraq to fight alongside the ISIL or other such Takfiri groups. The report added that the militants come from more than 80 countries which had not contributed to international terrorism before.

Syria has been grappling with a deadly conflict since March 2011. Western powers and their regional allies - especially Qatar, Saudi Arabia, and Turkey - are the main supporters of the militants operating inside Syria.

The ISIL terrorists currently control some parts of Syria and Iraq. They have been committing heinous crimes in the captured areas, including mass executions and beheadings.