A man was detained by worshippers at a west London mosque after he reportedly tried to attack people with a hammer.
Officers were called to the Darussalam Cultural Centre in Hayes Road, Southall, shortly after 04:30 BST.
The 38-year-old was arrested on suspicion of attempted grievous bodily harm. There were no reported injuries.
It was thought the man had been involved in a dispute with people who he believed were at the mosque the previous day, the Met Police said.