The man, who had not been identified, was taken to a hospital with life-threatening injuries, according to law enforcement officials investigating the episode. Hugh Carew, a Washington police spokesman, said the man was conscious and breathing when the authorities arrived.
Mr. Carew said initial reports indicated the man's burns were self-inflicted, but he said the police were investigating the matter. He said they had no idea what might have led the man to light himself on fire.
Witnesses called emergency operators shortly before 4:30 p.m. to report that a man was on fire as bystanders tried to extinguish the flames using their own clothing.
Some said they had spotted a gasoline canister on the Mall near the scene.
One witness, Emily Cherry, said she was not sure what was going on at first when she saw the flames.
"I kept thinking this is a stunt," she said.
