The 22-year-old, who is stationed at RM Condor in Arbroath, was reportedly stopped as he prepared to fly from California on a one-way ticket to Turkey, it emerged yesterday.
It is thought the man, a member of the Royal Marine Commandos, was planning to join Kurdish forces in their fight against IS extremists.
The marine was interviewed by Police Scotland as well as authorities in the United States, who said he had made contact with a Kurdish group online.
The group has links with both Turkey and the Iraqi city of Irbil, where Peshmerga (Kurdish) forces battling IS are based.
He is understood to have been picked up two weeks ago while trying to board a flight from Los Angeles to Istanbul.
The soldier serves with 45 Commando, which had been taking part in training and war games with US marines in the Mojave desert, California.
A Royal Navy spokesman said: “We are aware of an incident involving a Royal Marine who has recently been interviewed by Police Scotland.
“The matter is being investigated by the Royal Marines. It would be inappropriate to comment further.”
The Royal Navy said the marine was not facing any further police action.
A spokeswoman for Police Scotland declined to comment on the case.
It is thought hundreds of Britons have travelled to Iraq and Syria to take up arms with IS.
They include Abdul Raqib Amin, who grew up in Aberdeen and was pictured in a IS recruitment video earlier this year; and Aqsa Mahmood, a 20-year-old woman from Glasgow who travelled to Syria to live with jihadists.
She has used her blog to urge fellow Muslims to carry out terrorist attacks in Britain.
Terror experts have previously estimated that around 30 Scots have travelled to join the jihadists.
However, the prospect of a serving member of the armed forces travelling of their own accord to fight in Iraq or Syria is likely to cause considerable concern to the Ministry of Defence.
According to security sources who spoke to a newspaper, the capture of a UK soldier would lead to a “certain beheading” and a propaganda victory for the extremists.
A number of Britons are fighting with Peshmerga forces in Iraq – two were recently interviewed on TV – but it is unclear how many are in Syria.
Police, immigration and security officers are understood to be monitoring all UK flights to Turkey, leading some Britons planning to join fighters to travel to other European countries by ferry, coach and train before continuing to the Syrian border.
Turkey recently said it would allow Kurds to cross its border to join fellow fighters in beleaguered Kobani.
The city on the Syria-Turkish border has been the scene of fierce battles between Kurds – backed by US airstrikes – and IS.