The countries with the most fighters in the conflict are Tunisia, Saudi Arabia and Russia.

While around 6,500 Tunisians are reported to be fighting in Iraq and Syria, a further 5,000 have been stopped from leaving the country before they could join the fighting.

It can be assumed that the majority of the people who have travelled are with the Islamic State, according to the Soufan Group that collates the figures.

The group said that the figures may include women and children, who usually do not fight in the conflict. There are also unreported numbers of people who have died in or returned from the conflict zone.

While national governments do not know precise counts of their nationals who have gone to fight, estimates have been gathered by the United Nations, the Soufan Group and the International Centre for the Study of Radicalisation.

The Soufan Group published a paper on foreign fighters in June 2014, when 12,000 people had left - half the number in the current estimates.