Sinn Féin leader Mary Lou McDonald has launched High Court proceedings against RTÉ.

Deputy McDonald lodged papers in the case yesterday.

It has not yet been confirmed specifically what the action relates to; however, it is believed to be an allegation of defamation against the national broadcaster.

Neither RTÉ nor Sinn Féin is commenting publicly on the matter; however, a RTÉ News article published today suggests the proceedings relate to "a radio interview about a rally organised by the National Women’s Council outside Leinster House in early March.”

A Sinn Féin spokesperson said: “This is now a matter in litigation before the courts and it would be inappropriate to comment.”

Deputy McDonald is being represented in the case by Dublin solicitors McCartan & Burke.

Additional reporting from Frank Greaney.