Joe Robinson, 24, from Leeds, previously fought against the Islamic State group in Syria alongside the YPG Kurdish militia which Ankara deems to be a terror group.
He was holidaying with his girlfriend in the resort town of Didim in Aydin province in Turkey this week when he was detained. He has been remanded in custody ahead of a court trial, the state-run Anadolu news agency reported.
His girlfiend, a Bulgarian citizen, was detained with him but she was later allowed by the court to go free under judicial control. Her mother was also detained but freed without charge.
Anadolu said Robinson was arrested after posting pictures on social media allegedly showing himself in camouflage gear taking part in Kurdish People's Protection Units (YPG) operations in Syria.
Ankara considers the YPG a terrorist group and the Syrian branch of the Kurdistan Workers' Party (PKK), which has waged an insurgency inside Turkey since 1984.
But Washington considers the YPG as the main fighting force on the ground in Syria against IS militants.
The United States is now openly arming the YPG and the group is heavily involved in the US-backed operation to oust IS from their stronghold of Raqqa.
The YPG has also attracted the services of foreigners - many with no Kurdish family origin - to fight against IS in Syria and Iraq. Several have lost their lives.
The BBC reported Robinson is from the northern English city of Leeds and his fiance is Mira Rojkan.
It said Robinson, who is originally from Lancashire, spent five months fighting as a volunteer with the YPG against IS. He had previously described his experiences in media interviews, including with the Guardian.
Anadolu said that Turkish police launched the raid to arrest him after receiving a tip-off by email.
The Foreign Office in London said: "We are aware of the detention of a British national in Turkey and have requested consular access."
A Turkish defence official said: "The YPG is the PKK by another name and the PKK is considered a terrorist organisation not just by us but the UK as well. Of course anyone fighting with a terrorist organisation will be investigated and there is a strong possibility of charges and a long sentence if he is found guilty."
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