A van driver yesterday ploughed into crowds of pedestrians on Barcelona's most popular street in broad daylight.
"The United States condemns the terror attack in Barcelona, Spain, and will do whatever is necessary to help. Be tough & strong, we love you!" Trump said in a tweet yesterday.
In another tweet, he referred to an American general for taking tough attitude towards terrorists.
"Study what General Pershing of the United States did to terrorists when caught. There was no more radical Islamic terror for 35 years!"
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"This latest attack, the worst terror attack on Spanish soil since the 2004 Madrid train bombings, shows us again that radical Islamic terrorism is one of the greatest threats that we face in the world ... Whoever is responsible should know that the US, together with our allies, will find and punish those responsible, and drive the evil of radical Islamic terror from the face of the earth," he said.
Pence said this at a joint press conference with the president of Panama where he is travelling now.
Secretary of State Rex Tillerson said that the US is monitoring the situation and the country is ready to assist law enforcement and national security authorities in Spain.
"Our consulates in Barcelona and our entire Mission Spain team are currently assisting Americans in Spain who are affected by these events. We ask US citizens in the area to let your loved ones know you are safe. Terrorists around the world should know the United States and our allies are resolved to find you and bring you to justice," he said.
"Terrorists will not break our strength or our spirit. While we wait for further news, may the people of Barcelona know that the United States stands in solidarity with them at this dark hour.The US will continue to fight shoulder-to- shoulder with Spain against the vile scourge of terror," she said.
It's horrific to again see graphic images of innocent victims hit by a car that was driven by hate, Senator Dianne Feinstein said.
"This attack is yet another reminder that we must do more to combat all forms of extremism. Terrorists need to be identified and stopped before they are able to commit an attack," she said.
"The brutal and cowardly attack on innocent people at Las Ramblas today is a reminder that we are all obligated to stand against violence and hatred wherever it lives," said Los Angeles Mayor Eric Garcetti.
"The perpetrators of this heinous attack must be brought to justice, and we will not rest until the purveyors of hate and terror around the world are defeated," said the House Democratic Whip Steny H Hoyer.