A man has been arrested on suspicion of attempted murder after a stabbing inside a central London mosque.
The victim, in his 70s, was injured in an attack at London Central Mosque, near Regent's Park, which police are not treating as terror-related.
He was taken to hospital by paramedics where his condition has been assessed as non-life threatening.
A 29-year-old man was apprehended by worshippers who broke from prayer to restrain him until police arrived.
In a statement, the mosque said the injured man was the muezzin, the person who makes the call to prayer, and he had been stabbed shortly after 15:00 GMT during afternoon prayer.
The mosque's director general, Dr Ahmad Al Dubayan said he had a brief phone conversation with the muezzin in hospital, who said he was "okay and feeling well".
Ayaz Ahmad, an adviser to the mosque, said the stabbing "would have been life-threatening if it wasn't for the worshippers".
Images from inside the mosque showed a man wearing a red hooded top, jeans and with bare feet being pinned to the floor by police officers.
One video showed a knife on the floor under a plastic chair.
Mustafa Field, director of the Faiths Forum for London, told reporters the attack was "one stab, one strike, around the neck" of the victim.
He said: "Then the congregation members, some of them broke their prayers, and intervened, restrained the individual."
Abi Watik, who witnessed the attack, said the arrested man had been seen at the mosque previously and the muezzin was stabbed once in the shoulder.
"He was praying behind him [the muezzin] and then he stabbed him.
"He was waiting for him I think to start praying. He was right behind him."
The 59-year-old added that the suspect "was silent the whole time".
Dr Al Dubayan said: "We are so sad about what has happened and we hope it's just one off incident, not related or motivated by any kind of hatred."
Miqdaad Versi, from the Muslim Council of Britain, said: "It is deeply concerning that this has happened... Given other recent attacks elsewhere, many Muslims are on edge," he said.
Police believe the attack was an isolated incident and have increased patrols around the area to "provide reassurance to worshippers and the local community".
Ch Supt Helen Harpe said: "A 29-year-old man was arrested at the scene and he has been taken into custody.
"The man is believed to have been attending prayers inside the mosque.
"This incident has undoubtedly caused a great deal of concern and we are working as swiftly as possible to establish the circumstances."
Prime Minister Boris Johnson tweeted he was "deeply saddened" by the stabbing and his "thoughts are with the victim and all those affected".
Mayor of London Sadiq Khan said the Met Police would be "providing extra resources in the area" following the attack.
"Every Londoner is entitled to feel safe in their place of worship," he tweeted.