Political leaders in Northern Ireland have expressed revulsion after the Barcelona terror attack.
Sinn Fein's leader in the north Michelle O'Neill said it was horrific.
DUP chief Arlene Foster described it as barbaric.
A number of holidaymakers from Northern Ireland were near the Catalan city's Las Ramblas boulevard when a white van smashed into people at speed on Thursday.
Mrs O'Neill said: "The horrific attack in Barcelona was an appalling and indiscriminate slaughter of men, women and children.
"The scale of the devastation caused is heart-breaking.
"It is sickening to think that people deliberately set out to kill and maim people who were simply out enjoying a summer evening in one of the world's most beautiful and welcoming cities."
A book of condolence at Belfast City Hall is due to open later and will be signed by Lord Mayor Nuala McAllister.
Mrs Foster tweeted her solidarity with the injured and the forces of law and order.
"Horrific scenes. Barbaric act."
Alliance Party deputy leader Stephen Farry said it was important to stand together across Europe against those who sought to undermine open and diverse societies.
"In doing so, we must respond in a manner that defends these values that are so under threat."
SDLP leader Colum Eastwood said it was terrible news.