President Higgins has signed the book of condolence in Dublin
Flags are flying at half-mast on all government and official buildings today, as a mark of respect for those killed in the Brussels terror attacks and the tragic deaths in Buncrana.
President Michael D Higgins has signed the book of condolence at the Belgian embassy in Dublin.
While the Lord Mayor of Cork also opened a book of condolence at Cork City Hall for the victims.
It will be available for signing for two weeks during regular office hours.
It comes after 34 people died at terror attacks in the Belgium capital.
Explosions went off at Brussels airport and Malbeek metro station, for which the Islamic State claimed responsibility.
Two of the bombers who carried out the twin deadly attacks in Brussels were brothers and known to police.
While another suspect has reportedly been captured in the city's Anderlecht district.
It comes as the Department of Foreign Affairs says Irish citizens planning travel to Brussels are advised to delay non-essential travel until the situation has stabilised.
It also updated travel advice for both Belgium and France, asking people to exercise extreme caution.
President Michael D Higgins has described the attacks as 'desperate, hopeless and useless'.