A teenager is being questioned by counter-terrorism police in connection with three Britons who secretly went to fight in Syria.
The 19-year-old man from Coventry was arrested on Wednesday on suspicion of failing to disclose information about acts of terrorism in connection with the disappearance of Ali Kalantar, Mohammed Ismail and Rashid Amani, West Midlands Police said.
The three men from the Midlands city travelled to the Middle Eastern country in March 2014.
A police spokesman said: "They were believed to be engaged in the conflict; Kalantar and Amani have since been reported killed in the fighting."
WMP said the teen was being questioned under section 38 of the Terrorism Act 2000 at a West Midlands police station and there was no risk to the public.
In May an associate of Kalantar and Ismail was jailed for six years for making determined efforts to join Islamic State in Syria to fulfil his ambition of becoming a martyr.
Fanatic Zakariya Ashiq, 20, left the UK on November 6 last year on a bus from Victoria Station in London and made his way via Amsterdam, Frankfurt and Bulgaria to Jordan, his Old Bailey trial heard.
But when he failed to cross the border to reach his intended destination of Syria, he flew back to Heathrow where he was arrested on November 20.
The court heard he had WhatsApp conversations with the two men in which he described hitch-hiking and sleeping in mosques during his journey across Europe to join them.