"We estimate that - from late 2011 to 10 December 2013 - between 3,300 and 11,000 individuals have gone to Syria to fight against the Assad government," said the International Centre for the Study of Radicalization (ICSR), a partnership of five universities based at King's College London.

The ICSR said those sources indicated that most had fought for al-Nusra Front and the Islamic State of Iraq and the Levant, two main branches of al-Qaeda in Syria.

The study center said it used 1,500 sources, including media reports, government estimates, statements by the militants and social media to collect the data.

The report showed that Arabs and Europeans made up the bulk of foreign fighters, with up to 80 per cent, but militants from southeast Asia, North America, Africa, the Balkans and countries of the former Soviet Union were also represented.

Western Europeans, with the largest contingents from France and Britain, represent up to 18 per cent of the foreign fighters in Syria, it said. Up to 70 percent were from the Middle East.

However the report contradicts with earlier reports conducted by American and European research centers and gives far less numbers.

A report by the American Pentapolis Agency of statistics on September showed at least 130,000 non-Syrian militants were fighting in Syria.

On November 5th, Syrian Deputy Foreign Minister Faisal Muqdad announced that according to their findings, Turkey has let militants from 83 countries to enter Syria to topple the government.

The war in Syria started in March 2011, when pro-reform protests turned into a massive insurgency following the intervention of Western and regional states.

The unrest, which took in terrorist groups from across Europe, the Middle East and North Africa, has transpired as one of the bloodiest conflicts in recent history.

According to the United Nations, more than 120,000 people have been killed and millions displaced due to the turmoil that has gripped Syria for over two years.

SHI/SHI