An elderly man has been stabbed at a mosque in central London during afternoon prayers.
The man, in his 70s, was taken to hospital after he was stabbed at London Central Mosque in Regent's Park just after 3pm.
Police said he is in a non-life threatening condition after being treated at the scene and taken to a major trauma centre.
He is believed to be the muezzin who leads the call to prayer and was at the front of the hall when he was stabbed.
Met Police said a 29-year-old man was arrested at the scene on suspicion of attempted murder after worshippers pinned him down.
About 200-300 people are understood to have been in the mosque when the attack happened.
Video taken by people at the mosque showed a white man wearing a red hoodie, black trousers and no shoes being handcuffed by police.
One video showed a knife on the floor under a plastic chair.
Witnesses said he spoke with "a London accent" and had been a regular in the mosque but was last seen at least six months ago.
Abi Watik, 59, said: "We were shocked we didn't know what was happening."
He said the muezzin was stabbed once in the right shoulder moments after prayers started.
Prime Minister Boris Johnson tweeted: "I'm deeply saddened to hear of the attack at the London Central Mosque. It's so awful that this should happen, especially in a place of worship. My thoughts are with the victim and all those affected."
Met Police say the incident is not being treated as terror related.
London Central Mosque is one of the country's largest and can hold 5,000 worshippers, with people from across London travelling to it for prayers every day.
Sky News' Inzamam Rashid said having spoken to people at the scene "there are heightened fears for Muslims at places like Regent's Park Mosque and there will be heightened security in the days to come".