A British man who fought as part of the Syrian Democratic Forces (SDF) has criticised the United States' decision to pull troops out of north-eastern Syria.
Macer Gifford fought in the SDF for three years against so-called Islamic State (IS) which once controlled large swathes of the country.
The Kurdish-led SDF have worked closely alongside American troops in Syria to defeat IS.
But there are fears that US President Donald Trump's decision could leave the SDF vulnerable to attack from Turkey or a resurging IS.
Turkey, a member of NATO, views the Kurdish forces as a terrorist organisation.
Around 50 of the 1,000 US troops based in Syria have so far been withdrawn.
Mr Gifford slammed the decision as a "betrayal".
"The Kurds have lost 11,000 men in the fight against extremism in Syria," he said.
"To have Donald Trump pull out troops and to green-light a Turkish invasion - it is a real betrayal of their suffering and of course it risks our security at home, as well."
Mr Gifford, who finishing fighting with the SDF in Raqqa, says he knows Kurds in Syria are frightened of a potential Turkish invasion.
"A lot of people are worried. People are locking their doors, a number of people have left their home already, there are hundreds of thousands of refugees already in those areas," he said.
"There are millions of Kurds who have not actually suffered for years because of the efforts of the Americans, the Brits and the SDF.
"So, to have war come to them for such a foolish reason, because of so-called 'security concerns' by Turkey, is a real stab in the back."
Mr Trump warned Turkey he would "obliterate" its economy should it do anything "off limits".
The decision to withdraw has been heavily criticised - even by loyal Republicans.
A former US military chief said it raises concerns about America's "level of commitment" to its partners and allies.
Meanwhile, Tom Tugendhat, the chair of the UK Foreign Affairs Committee, admitted the withdrawal and "any imminent Turkish military operation could trigger a large-scale humanitarian crisis".
Concerns have been raised that the exit of American troops could also leave space for IS to return.
Mr Gifford believes the withdrawal will see a power vacuum and problems for the SDF.
"The SDF will start to splinter slightly, some groups might start falling in line with Assad, others wall fall in line with Turkey, others will choose to stay with the Kurds," he said.
"There will be a vacuum which will only be filled by so-called Islamic State.
"There will be gains made by Assad and Iran and other countries like Russia, as well.
"You'll see a partitioning of everything that the Americans and Brits have fought for over the past four years and of course a spike in violence."
Britain began fighting IS in Syria from the air in 2015 as part of a coalition of nations, including the US and France.
The air campaign, known as Operation Shader, began in Iraq the previous year and has seen British fighter jets fly near-daily missions against IS.