At least one American was among the 14 killed in vehicle-ramming attacks in Catalonia, Spain, over the past two days, according to U.S. Secretary of State Rex Tillerson.
Tillerson said Friday that the Department of State had "received word and confirmed the death of one American citizen in the terrorist attack in Spain." U.S. officials are "still confirming the injuries and deaths of others," he added.
"Hate is not an American value," Tillerson told reporters.
Spanish authorities said they have detained four people in connection to both the incident in Cambrils early Friday that killed at least one person and the vehicle attack Thursday in Barcelona that killed at least 13. More than 100 others were injured.
Tillerson did not specify which attack killed the American citizen.
Those injured and killed in the separate attacks represented at least 34 different nationalities, according to a preliminary assessment by Catalan police, a sign of the area's popularity with tourists from around the world.
Spanish Prime Minister Mariano Rajoy on Thursday expressed solidarity with the victims and their families, describing the attack in Barcelona as "jihadist terrorism."
Those responsible for the rampage will be brought to justice, he said, stressing that the response to terrorism must be global.
Rajoy said Barcelona residents are suffering "the same pain and the same uncertainty" as their neighbors in Madrid, Paris, Nice, Brussels and London, referencing other European cities that have also been subject to deadly terror attacks.
ABC News' Erin Dooley contributed to this report.
This is a breaking news story. Check back for updates.