Political figures, institutions and governments from around the world on Thursday condemned a terror attack in the Spanish city of Barcelona that killed at least 13 people and injured 50 when a van mowed over pedestrians in the downtown Rambla boulevard.

President Trump condemned the attack in a Twitter post. “Be tough & strong, we love you!,” he wrote.

In a following post, he praised the counterterrorism tactics of a U.S. general in the Philippines in the early 1900s. Most historians say that the methods were unproven legends and that even if they were used, they did not work, as reported in The NY Times.

The mayors of European capitals that had been hit by similar attacks involving vehicles plowing into crowds were quick to express their solidarity with the victims via various social media platforms.

"My thoughts are with the victims of this barbaric terrorist attack in the great city of Barcelona and with their brave emergency services," said Sadiq Khan, the mayor of London, which has seen three similar attacks this year involving vehicles running over pedestrians since March.

"London stands with Barcelona against the evil of terrorism," Khan added on his official Twitter account.

Anne Hidalgo, the Spanish-born mayor of Paris _ a city that has seen multiple terror attacks in the past few years _ expressed her "sadness and outrage" over the act and sent her support to the victims and their loved ones.

"Barcelona and Paris are cities of sharing, of love and of tolerance. These values are stronger than this odious and cowardly terrorism," said Hidalgo.

"I also extend a message of solidarity to my friend (Barcelona Mayor) Ada Colau and all locals. Parisians are on their side," she added.

The mayor of Stockholm, Karin Wanngard, also extended her condolences; downtown Stockholm was the scene of a truck-ramming attack in April.

"Deeply saddened about the attack in the beautiful city Barcelona. My thoughts are with all affected. We need unity now more than ever," said Wanngard.

Meanwhile, German Chancellor Angela Merkel said through her spokesman Steffen Seibert that Germany was "in deep mourning for the victims of the repulsive attack in Barcelona and on the side of Spaniards in solidarity and friendship."

The United Kingdom's prime minister Theresa May, said in a statement: "My thoughts are with the victims of today’s terrible attack in Barcelona and the emergency services responding to this ongoing incident. The UK stands with Spain against terror."

"Terrible reports from Barcelona. My thoughts are with those killed and injured, and the emergency services working to save lives," tweeted the UK's leader of the opposition Labour Party, Jeremy Corbyn.

The United States' secretary of state, Rex Tillerson, also offered his support to authorities in Spain regarding the investigation into the attack.

"Terrorists around the world should know the United States are resolved to find you and bring you to justice," said Tillerson during a press conference, as he urged US citizens in the Spanish coastal city to contact family members to let them know they were safe.

Latin American nations were quick to express their solidarity with the victims of the atrocity, with leaders and government representatives of Mexico, Panama, Honduras, Costa Rica, Guatemala and Ecuador condemning the act.

The European Union, for its part, joined in with the outpour of solidarity, with President of the European Commission, Jean-Claude Juncker tweeting: "My deepest condolences to the families and loved ones of the victims, to (Spanish Prime Minister) Mariano Rajoy and the people of Spain."

European Council President Donald Tusk meanwhile tweeted: "Our thoughts are with the victims and all affected by this cowardly attack on innocents."

The attack prompted the UK's Foreign Office and the US State Department to issue warnings for their respective citizens visiting Barcelona, advising them to stay away from the area where the attack took place.

"US citizens in Barcelona are urged to avoid the areas and to follow local media and other information sources for additional guidance," read a statement released by the US Consulate in Barcelona.

Back in Spain, Rajoy took to Twitter on his way to Barcelona to offer the following words to the nation: "The terrorists will never defeat a united people that loves freedom over barbarism. All of Spain is with the victims and their families."