A converted Muslim is being questioned by detectives over alleged threats to kill US President Barack Obama during his trip to Ireland.
Khalid Kelly, who is in his 40s, was detained over claims made in a newspaper article.
A Garda spokesman said officers from the Special Detective Unit investigating threats to kill or cause harm searched a home in Dublin's north inner city on Thursday morning.
Mr Obama is due to visit Dublin and his ancestral home Moneygall, Co Offaly, later this month.
Security surrounding the President has been stepped up in recent weeks after a special forces team killed al Qaida chief Osama Bin Laden.
The suspect is being detained in Store Street Garda station under the provisions of Section 30 Offences Against the State Act 1939 as amended.
He can be held for up to three days.