A fight broke out between English Defence League supporters and local youths outside East London Mosque leading to fifteen arrests on Saturday.
Several hundred people were involved in a larger disturbance following the fight on Whitechapel Road in the late afternoon.
The Metropolitan Police spokesman said the arrests were made to prevent a breach of the peace.
Witnesses told EastLondonLines that bottles and other objects were thrown at the mosque and that police had arrested members of both sides involved in the fight, though the Met could not confirm this.
EDL supporters are believed to have travelled to Whitechapel from Barking after attending an earlier demonstration there organised by the far-right group.
Police and ambulance were called to the area at 4.55pm after reports of a large fight and a man suffering injuries that were not life-threatening. He was then taken to hospital.
The Met spokesman added: “We are not aware of further significant injuries.”
The men have all been released without charge, and police in Tower Hamlets are currently investigating the incident.
The East London Mosque Trust was unavailable for comment.