Lionel Messi and Cristiano Ronaldo are among the football stars to post messages of solidarity on social media following the terror attack in Barcelona on Thursday.
Catalonia interior minister Joaquim Forn confirmed that 13 people were killed and at least 50 injured when a van drove into pedestrians on Las Ramblas, a packed street in the city popular with tourists.
Local police confirmed two people had been arrested in connection with the incident, which they said they were treating as an act of terrorism.
Barca star Messi was among the first players to respond, writing via his official Instagram page: "I want to send my condolences and all my support to the families and friends of the victims of the terrible attack in our beloved Barcelona.
"We are not going to give up. There are many more of us who want to live in a world of peace, without hate and where respect and tolerance are the bases of living together."
Striker Luis Suarez, defender Gerard Pique, Madrid forward Ronaldo and club captain Sergio Ramos also expressed their condolences.
"Dismayed at the news coming out of Barcelona. All support and solidarity to the families and friends of the victims," Ronaldo wrote.
There were similar messages from the official Twitter accounts of clubs across Spain and the world, including Barca, Madrid, Atletico Madrid, Manchester United and Paris Saint-Germain.
Neymar, who left Barca to join PSG in a world-record deal this month, tweeted: "May God comfort all the families. I love you Barcelona."
The Royal Spanish Football Federation has suggested a minute silence be held prior to matches in all domestic competitions over the coming weekend.
