A child with British nationality is believed to be among those unaccounted for following the Spain terror attacks, Theresa May has said.

The Prime Minister said UK authorities were "urgently looking into reports" that the child, who has dual British nationality, is missing.

She spoke after the grandfather of Julian Alessandro Cadman made a plea for information about the boy, who became separated from his mother during the attack in Barcelona.

Tony Cadman, whose Facebook profile says he lives in Sydney and is from Gillingham, Dorset, posted a photograph of Julian, writing: "My Grandson, Julian Alessandro Cadman is missing. Please like and share."

The death toll from the atrocities in the Catalan capital and later in the town of Cambrils has risen to 14, with "a number" of Britons believed to be among the 130 people injured.

Speaking from her country residence Chequers, the Prime Minister said: "The UK stands shoulder to shoulder with Spain in confronting and dealing with the evil of terrorism, and I have offered any assistance we can provide.

"Sadly I must tell you that we do believe that a number of British nationals were caught up in the attack and we are urgently looking into reports of a child believed missing, who is a British dual national."