Enda Kenny has signed a book of condolence for the victims of Wednesday's Westminster terror attack.
The Taoiseach expressed sympathies for the families of those who lost loved ones.
He visited the British embassy in Dublin to write a personal message of support for Prime Minister Theresa May and her Government following the tragic events in London.
Three people were killed when Khalid Masood's car on ploughed into them on Westminster Bridge.
Masood then stabbed police officer Keith Palmer near Parliament.
The Irish Republic's head of state, President Michael D Higgins, is to write to the Queen of England and London Mayor Sadiq Khan to express the sympathy "of the Irish people with the families of those who have lost their lives and to those who have been injured".