Gerry Adams has been warned of a "credible" death threat, Sinn Fein said.
The message was passed to the PSNI by Mr Adams' wife while he was not at home.
Mr Adams, was released last night after four days of questioning about the notorious 1972 killing of Jean McConville and other alleged links with the IRA.
Adams attacks reasons for his detention and denies McConville murder
It is claimed IRA volunteers described what happened the night Jean McConville was murdered to Boston College's "Belfast Project".