The British Prime Minister has said UK authorities are “urgently” looking into reports of a missing child following the Spanish terror attacks.
In a statement, Theresa May said she believed a number of British nationalities were caught up in the attack.
She said the missing boy had dual nationality; however she did not name him.
At least 14 people have died and 130 more are injured following the two separate attacks in Barcelona city centre and the town of Cambrils close to the city.
One Irish family was caught up in the attack.
Husband and wife, Norman and Pederlita Putot are Irish citizens who are originally from the Philippines. They were holidaying in the Catalan capital alongside their two Irish-born children, Nathaniel and Pearl.
Five-year-old Nathaniel sustained serious injuries - including a broken femur - in the attack. Mr Putot was also hurt.
The family are currently recovering in hospital and their injuries are not believed to be life threatening.
In a statement on Friday afternoon, Mrs May said: Sadly, I must tell you that we do believe that a number of British nationals were caught up in the attack.
"We're urgently looking into reports of a child believed missing, who is a British dual national," she said.
She said the British Foreign Office is offering consular assistance to the victims of the attack and is “working urgently to see if there are others” who need help.
She added that "terrorism is the great threat we all face."
Missing Australian child
Earlier it was reported that a seven-year-old boy from Australia is missing in Barcelona after his mother was badly injured in the attack.
7-year-old Julian Alessandro Cadman
ABC News in Australia said Julian Cadman was separated from his mother in the confusion.
His mother was taken hospital in a serious condition and the boy’s family shared a picture of him in a bid to find him.
An Australian government spokesperson said one citizen remains unaccounted for and three were injured.
The attacks affected citizens from 34 countries, according to the Spanish Civil Protection Agency.
An Italian man, 35-year-old Bruno Gulotta, a father of two, was the first victim to be named.
He was strolling down the boulevard with his partner and two sons when he was hit by the van, Italian reports said. The rest of the family were uninjured.
Another Italian was among the dead and three were injured, officials in Rome said.
The French foreign ministry has said 26 of its citizens were injured in the attacks - 11 of them seriously.
A foreign ministry spokesman in Berlin said they know of 13 Germans injured - "some of them seriously, so seriously that they are still fighting for their lives."