The recently elected party leader insisted Spanish police must “act appropriately” or Catalonia will break away from Spain.
Mr Bolton added TV and social media footage of the aggression during the disputed independence referendum had been “horrific”.
Speaking to RT, he said: “I would say that if the Spanish authorities are keen on dealing with this issue and making sure that Catalonia doesn’t break away, then the police have to act appropriately.
“Some of the scenes that we saw on the television and some of the scenes coming across on social media were quite horrific in showing the manner in which some of the Spanish police were treating innocent and peaceful people queuing up to vote.
“I don’t think that helps anybody at this stage. They need to be discussing a mutually agreeable way forward now.
“But that may be difficult given the violence that we’ve seen.”
The EU is scrambling to avoid a Catalexit, which would see the bloc disintegrate further after an already-chaotic 18 months.
More than two million Catalan voters braved police brutality, which left 800 injured, to choose independence for Catalonia in Sunday’s disputed referendum, according to Catalan authorities.