Two teenagers have been arrested on suspicion of arson after a large fire engulfed part of a south London mosque which is said to be the largest in western Europe.
Shocked onlookers watched dozens of firefighters tackle the blaze at the Baitul Futuh mosque in Morden on Saturday.
Two boys aged 14 and 16 have been arrested on suspicion of arson, and both remain in custody at a south London police station, Scotland Yard said.
A man was taken to hospital suffering from smoke inhalation, and London Fire Brigade said the blaze had hit admin buildings though the ''mosque itself is thankfully unaffected''.
People gathered opposite the mosque, watching a dark plume of smoke billowing out of the building's roof, before they were ushered behind a police cordon.
A member of the public reported the blaze at 12.06pm.
The mosque was built for the Ahmadiyya Muslim community to provide people with a meeting place and somewhere to hold social religious events.
It was built on the site of the old Express Dairies in 1999. The building bears the Ahmadiyya Muslim motto ''Love for all, hatred for none''.
Merton Council leader Stephen Alambritis described the mosque as a ''major landmark'' in the area.
Damage to the ''beautiful building'' will be a ''big blow'' to the community, he said.
Mr Alambritis said the mosque is a very secure building which is manned by security staff.
The MP for Mitcham and Morden, Labour's Siobhain McDonagh, spoke of her shock at news of the fire.
''The mosque does a huge amount for the local community. They are tireless raisers of funds for charity - their own charities' funds and charities in the community,'' she said.
Police, London Ambulance and 10 fire engines attended the scene and the A24 London Road was partially closed, causing traffic tailbacks.
British Transport Police were at Morden South overground station, adjacent to the mosque, where trains were running at reduced speed and passing through the station without stopping.