South Wales Police have confirmed that they are treating a fire which broke out at a Cardiff mosque as suspicious.
Nobody is believed to have been injured by the fire
Fire crews and police were alerted just before 0830 GMT to the blaze at the Madina Mosque in Cathays. The fire on the second floor spread to the roof.
Central Cardiff MP Jenny Willott, who was at the scene, described the fire as "really shocking".
Police are appealing for information about a man said to be of Middle Eastern appearance seen in the area.
He is described as being in his 20s and of medium build. He was wearing a dark hat and a dark coat.
Firefighters have now brought the blaze under control
The road with the mosque has been cordoned off and a police sniffer dog team brought in and investigators are now at the scene to determine a cause.
A command room has also been set up at Cardiff Central police station.
Superintendent Bob Tooby said it appeared there was more than one seat of fire and that was being investigated by both police forensic scientists and the fire service.
"There's every possibility accelerants were involved but it's too early to say. All the tests need to be carried out forensically," he said.
A spokeswoman for South Wales Fire Service said at least a quarter of the building has been severely damaged by the fire.
Officers said it was too early to tell if the suspected arson was racially motivated.
Mosque spokesman Javed Javed said they were waiting for the police and fire brigade reports on the blaze.
He said: "As to who the culprits are, we are keeping an open mind and we cannot point fingers to any groups or person.
"The community has been very saddened by the fire. The way it looks, it has been deliberately started and that makes it more sad."
She said: "The mosque is a big part of the local community.
Ms Willott said it was upsetting for the local community to feel they were being targeted.
She said: "There have been some tensions within the mosque which have been reported recently.
"But nothing as serious that would ever have led us to believed this would happen."
South Wales Fire Service have four pumps and a hydraulic appliance at the scene and relief firefighters have also been called to help tackle the blaze.
The Welsh Ambulance Service said they were also there although no casualties were reported.
Network Rail has been informed as smoke from the fire is affecting the line at Queen Street station in the direction of Caerphilly and Llanishen.