A 25-year-old man from Derry has been charged with attending a weapons and explosives training camp in Syria and with possession of explosives with intent to endanger life.
The charges against Eamon Bradley from Melmore Gardens in the Creggan Estate in Derry are alleged to have occurred in Syria between April and October of this year.
A solicitor for Mr Bradley said his client intended to contest the charges.
The accused was remanded in custody until next month.
Mr Bradley told police he was involved in battles against both Islamic State and the government regime.
He gave detectives an extensive account of his role in the bloody conflict earlier this year, the city's magistrates court was told.
He appeared in court today charged under UK terror legislation with committing two offences in Syria - possession of explosives with intent to endanger life, namely a grenade, and receiving training in arms and explosives.
Dressed in a black T-shirt, bearded Mr Bradley, who the court heard converted to Islam five years ago, spoke only to confirm his date of birth and that he understood the charges he faces.
He was remanded in custody after his application for bail was refused by District Judge Barney McElholm.
A detective sergeant with the Police Service of Northern Ireland told the judge he could connect the accused with the charges.
He described to police contact with people he does not identify on the internet which assisted him to getting to the Syrian/Turkish border, which is a known crossing point into Syria for the on-going conflict.
The officer said Bradley, an Irish citizen, flew to Turkey from Dublin in February and stayed at various locations near the Syrian border for two months.
"That's where he learned more about Islam and various groups and groupings in the area," he said.
The officer said Mr Bradley told detectives he assembled with a group of men and went over the border into Syria via a river crossing.
Mr Bradley informed police that he attended a training camp under the control of a group called Jaysh Al Islam, which translated is Army of Islam.
He was there for a period of approximately two months.
Mr Bradley stated that he received training in this camp in AK47 firearms, he mentions other firearms, he also mentions mortars and other explosive weapons.
The detective added: During his account with police he stated he was actively involved in three battles in Syria - two against the Baathist regime and one against Isil.
In course of those battles he was armed with an AK47 and numerous magazines of ammunition and a grenade, he claimed
The officer said Mr Bradley had stressed to police that he did not use any of the weapons during the battles.
He said the accused told officers he was in a group of around 20 men who were armed with heavy artillery including mortars and tanks. He said the opposing side was similarly armed but also had planes.