Two British men who fought against the Islamic State in Syria were held for six hours after returning home for Christmas, but say their conflict with the terrorist group is "unfinished business."

The pair was questioned by counter-terrorism police at London's Heathrow Airport before being released, they have revealed.

Former soldiers Jamie Read, 24, and James Hughes, 26, are understood to have been fighting alongside Kurdish forces in Kobane on behalf of the Kurdish People's Protection Units (YPG).

The two claimed their laptops, phones, and equipment were confiscated and they were interviewed separately at Heathrow for six hours.

Taking up arms in a foreign conflict could be considered an offense under UK law, and British men have been jailed for terrorist offenses overseas.

However, Prime Minister David Cameron has previously said that that those fighting against the Islamic State would not be treated in the same way as those who had joined it.

Read told UK newspaper the Sun: "I was raging. They kept asking why we went, who we were with and were we being paid? We weren't, of course." Stating that the fight against the Islamic State is "unfinished business," Read said that he hoped to return.

The families of the soldiers have previously spoken out in support of their decision to join the conflict. Hughes' father David told Sky News that his son was "the epitome of a true blue Brit" and criticized legislation that could leave fighters in Syria stateless.

"We should all be proud of the choices and actions of these guys and all the armchair critics in the media and vote-grabbing pundits in government would do well to reconsider the facts before branding people as traitors or criminals, especially when they have clearly proven themselves already as heroes, David Hughes said."

The pair have been pictured on social media with US national Jordan Matson, who has previously publicly disclosed his involvement with the YPG.

They flew from Manchester to Istanbul before making their way to war-torn Kobane to fight alongside the Kurdish forces.

The former soldiers have always rejected claims that they were operating as mercenaries. The YPG reportedly provides weapons, uniforms, food, and accommodation to fighters but does not pay a salary or bear the costs of travel to Syria.

Read said he had lost 11 allies in the fight against the Islamic State. And in a written statement distributed on 30 November, a YPG spokesperson said that 11 fighters and three civilians were killed in explosions and subsequent clashes in a border gate area.