British police said they were not treating a London mosque stabbing, in which an elderly man suffered non-life threatening injuries, as terror-related.
The London ambulance service said the victim had been taken "to a major trauma centre" after the mid-afternoon attack.
"A 29-year-old man, who is believed to have been attending prayers, was arrested inside the mosque on suspicion of attempted murder," the London police said in a statement.
"The incident is not being treated as terror-related at this time."
The police said the victim was a worshipper in his 70s and his condition "assessed as non-life-threatening."
A statement issued by the London Central Mosque where the attack occurred said the assailant was apprehended by worshippers until the police arrived at the scene.
It said the mosque's Muazzin - a religious leader who calls the faithful to prayer - "did not sustain any life-threatening injuries but was seriously injured and is being treated at the hospital"
One witness said the man appeared to have been stabbed in the neck.
Prime Minister Boris Johnson tweeted that he was "deeply saddened" to learn of the attack.
"It's so awful that this should happen, especially in a place of worship. My thoughts are with the victim and all those affected," Johnson said.
Photographs shared on social media from inside the mosque in Regent's Park showed a white man in a red hooded top being pinned to the ground and handcuffed by two police officers.
The picture showed a group of male worshipper in their winter overcoats standing nearby and watching the scene.
One video showed a small knife lying under a plastic white chair next to the suspect.
Another showed the suspect being silently led escorted out of the mosque by police.
