An Garda Síochána's most senior anti-terrorist officer is to retire from the organisation.

In an unexpected move Assistant Commissioner Michael O'Sullivan is to leave the force at the end of March.

He has been responsible for state security and intelligence for the past three years and has overseen overt and covert operations against dissident republicans and the deportation of suspected Islamic terrorist here.

He was also the first Garda on the Interpol executive and led the Garda involvement in the repatriation of Lisa Smith.

Assistant Commissioner O'Sullivan will have served forty years in An Garda Síochána when he retires.

The Garda Commissioner has been informed.