The State Department announced Friday that one American was among the 14 people killed in a pair of deadly terror attacks in Spain.

The assaults -- in Barcelona and Cambrils -- wounded more than 100 others, and one U.S. citizen was also among that count, officials said.

Neither person's name was immediately released.

The news comes as a fourth person was arrested on Friday in connection with the terror attacks. Spanish police also announced that they are searching for four suspects connected to the attacks.

Police shot and killed five suspects who were equipped with bomb belts in Cambrils. The belts were found later to be fake. It was not immediately clear if the Barcelona van driver was among the arrested or dead suspects but police said they are investigating it.

Local government confirmed the incident in Cambrils was linked to the attack in central Barcelona.

The after effects of the vicious vehicle attack in Barcelona, which also wounded more than 100, were still being felt in the Spanish capital even as officials foiled a second extremist plot in an early morning shootout and hunted for other militants involved in the attacks.

In particular, the driver of the van remained elusive Friday as Spain conducted a major anti-terror operation to locate the man.

Fifteen of those injured on Thursday remained in serious condition and authorities warned the death toll could continue to rise.

Security forces mobilized quickly following the Barcelona attack, where authorities say a jihadist used a van to target people on one of the Catalonia capital’s most popular streets and managed to escape the scene by foot.

The injured and dead were from 34 different countries, including France, Germany, Pakistan and the Philippines, a government statement said. A U.S. man was unaccounted for, his family said.

ISIS claimed responsibility for the attack and said the perpetrators were “soldiers of the Islamic State,” the terrorist organization’s propaganda agency said.

"The perpetrators of the attack in #Barcelona are Islamic state soldiers and carried out the operation on command of [ISIS' leader] of targeting coalition countries," the statement read.

Spanish Prime Minister Mariano Rejoy, meanwhile, called the tragedy a "jihadist attack" and announced three days of official mourning, Reuters reported.

Initial reports in the Spanish media named Driss Oukabir, a French citizen of Moroccan origin, as the person driving the van after his identification documents were found in the vehicle used in the terror attack.

But shortly afterwards, the man turned himself in to police, denying any involvement in the terror plot and claiming his documents were stolen, possibly by his brother, La Vanguardia reported. Police haven't confirmed that the man's brother was the driver of the van.

It remained unclear how many people were involved in the terror attack.

Police have detained four people, including a Moroccan man, a man from Spain's autonomous African city of Melilla, and one man whose identity was unknown.

According to El Periodico, as Fox News reported earlier, the CIA warned local Spanish authorities two months ago about a possible terror attack, following a number of similar vehicular attacks across Europe, including in London, Nice, Berlin and Stockholm.

The latest terror attack was the deadliest attack in Spain since the 2004 Madrid train bombings that killed 192 people.

The Associated Press contributed to this report.