Volunteer fighting Daesh: 'The only way we can defeat them is with force of arms'

Macer Gifford went to Syria three years ago to volunteer first with the Kurdish militia, and is now fighting with an Assyrian unit, part of the US-backed forces battling IS.

The 30-year-old Briton has been questioned by UK and US government officials, but insists: "I am not a terrorist. I am here defending the people of Syria against terrorists."

At home, he has written and lectured about the complex situation in Syria, offering a first-hand experience of IS's evolving tactics, and believes the militants can only be defeated by sheer force.

"The Islamic State (group) is actually an exceptional opponent," he said. "We can't negotiate them away, we can't wish them away. The only way we can defeat them is with force of arms."

Along with two American comrades, he has been facing IS snipers on the front line in the ravaged city of Raqqa.

They are among several British and American volunteers involved in the battle for the city in north-eastern Syria that the militants declared the capital of their self-proclaimed caliphate.

The men joined US-allied Syrian militias for different reasons - some motivated by survivors' stories of the unimaginable brutality of IS; others joined what they see as a noble quest for justice and a final battle with the "heart of darkness", in a belief that violence can only be met with violence.

Taylor Hudson, a 33-year old from California, compares the fight for Raqqa to the 1945 Battle of Berlin in the Second World War that was critical to ending the rule of Adolf Hitler.

"This is the Berlin of our times," said Mr Hudson, who doubles as a platoon medic and a sniper. For him, IS extremists "represent everything that is wrong with humanity".

Syria's war, in its seventh year, has attracted foreign fighters to all sides of a complicated conflict.

Islamic extremists from Europe, Asia and North Africa have boosted the ranks of IS, as well as rival al Qaida-linked groups.

Shiite Iranian and Lebanese militias have sided with the Syrian government, deepening the sectarian nature of the conflict that has killed more than 400,000 people and displaced over 11 million, half of Syria's pre-war population.

On the other side - though far less in number than the thousands of foreigners who swelled IS ranks - most Western foreign volunteers have been drawn to the US-allied Kurdish militia known as the People's Protection Units, known as the YPG.

The US military has developed a close relationship with the YPG and its extension, the Syrian Democratic Forces.

Some Western volunteers have died in battle. Earlier in July the YPG announced that 28-year-old Robert Grodt, of California, and 29-year-old Nicholas Alan Warden, of New York state, had died in the battle for Raqqa.

Mr Hudson, who has been fighting in Syria for 13 months, said he was moved to tears by stories in the media of Iraqi Yazidi women enslaved by IS militants, and looked for a way to help.

A pharmacy student who learned combat medicine in the field, he said he had treated 600 wounded ahead of the march on Raqqa.

For Kevin Howard, a 28-year old former US military contractor from California who fought in Iraq in 2006, the war against IS is more personal.

A skilled sniper who prides himself in having killed 12 militants so far, Mr Howard said he is doing it for the victims of the Bataclan theatre attack in France, where the sister of one of his best friends survived.

The attacks on November 13 2015, claimed by IS, killed 130 people at Paris cafes, the national stadium and the Bataclan, where 90 died.

"This is a continuation of that fight. I think if you leave something unfinished, it will remain unfinished for a lifetime," he said.