Spanish Civil Guard officers break through a door at a polling station for the banned independence referendum where Catalan President Carles Puigdemont was supposed to vote in Sant Julia de Ramis, Spain October 1, 2017. REUTERS/Juan Medina

MANCHESTER, England (Reuters) - Britain is worried by violence during a banned referendum in Spain’s northeastern region of Catalonia but sees the vote as unconstitutional, Foreign Secretary Boris Johnson said on Sunday.

“We are obviously worried by any violence but clearly the referendum, as I understand it, is not constitutional so a balance needs to be struck,” Johnson told Reuters. “We hope very much that things will calm down.”