The Ministry of Defence confirms it is investigating reports that a soldier has left his Cyprus base to join Kurdish peshmerga forces fighting militants from the Islamic State group in Syria and Iraq.
Defence authorities refused to name the man, who is reported to be 19 years old.
If the reports are confirmed, he would be the first serving British soldier to travel to fight Islamic State (IS), and an obvious target for the militant group.
However, it would not be the first time British people with a connection to the army have travelled to the region apparently to fight.
In November 2014 reports said former soldiers Jamie Read (pictured) and James Hughes had gone to Syria to battle Islamic State – although it has been suggested theydid not take part in frontline battle.
And people from the British Kurdish community have for many years travelled to fight with Kurdish militias.
On Thursday the United States and Turkey signed an agreement to train and equip moderate Syrian opposition fighters.
The US military has said it is planning to send more than 400 troops, including special operations forces, to train Syrian moderates at sites outside Syria as part of the battle against IS. Saudi Arabia and Qatar have offered to host training sites.
Turkey hopes the initiative will bolster a weakened and divided Syrian opposition in its fight against the Syrian regime of President Assad.