World Bulletin / News Desk
The 30-year-old was arrested in Somerset, southwestern England, by counter-extremism police from London.
In a statement the Metropolitan Police, which leads counter-extreme operations around the country, confirmed the suspect was a serving member of the armed forces and said there was no immediate threat to the local community.
The statement did not specify to which branch of the armed forces the suspect belonged.
Searches were being carried out at a property and a wooded area in south Devon, near Somerset, and in Larne, Northern Ireland.
The BBC reported the searches were connected to two arms caches found near Larne earlier this year.
The arrest comes at a time of heightened awareness of extremist groups in Ireland and the U.K., where both nationalist and pro-British loyalist extremists remain active.
In May, the U.K. raised the threat level from dissident nationalist extremists for the first time since 2012.