LONDON (Reuters) -British police arrested Graham Smith, leader of an anti-monarchist group Republic, ahead of King Charles' coronation on Saturday, a spokesperson for the group said.

London police chief Mark Rowley had warned on Friday that there would be a "very low tolerance for disruption" on the streets in central London where tens of thousands of people have gathered to watch the royal processions.

Police did not confirm the arrest, saying they did not immediately name those arrested.

A photo posted on Twitter showed Smith sitting on the ground surrounded by a group of police officers. An officer at the scene near Trafalgar Square said three republican protesters had been arrested for carrying paint.

More than 11,000 police officers are on patrol for the coronation, the biggest ceremonial event staged in the British capital for 70 years.

Rowley said ahead of the event that police would take action if protesters tried to "obstruct the enjoyment and celebration" of a significant number of people.

(Reporting by Andrew MacAskill, writing by Sarah Young; editing by Michael Holden and Kate Holton)