A man who Egypt described as embracing "extremist ideas" was detained on Tuesday near the US Embassy in central Cairo after a bottle containing flammable chemicals caught fire in his backpack.
The incident caused no casualties and the embassy said on its Twitter account that it was resuming normal business after police finished their investigation at the scene.
A statement released by Egypt's state information service named the suspect as 24-year-old Abdullah Ayman Abdesamea.
"Preliminary investigations suggest that he embraces some extremist ideas and was intending to use them to commit an act of aggression," the statement said.
A witness said she heard a blast and then saw a man with a backpack that had caught on fire close to the Semiramis Hotel, across the road from the embassy premises.
The man was then thrown to the ground by security forces as the fire was extinguished, the witness said.
CCTV footage posted on social media appeared to show the man crossing the street before falling to the ground under a puff of smoke.
Egyptian security forces detained a man on Tuesday after an explosive device detonated near the U.S. Embassy in central Cairo, No casualties were reported. pic.twitter.com/hfuJ2c2Hrv
— News_Executive (@News_Executive) September 4, 2018
Another video circulating showed a man in a black T-shirt kneeling on the road amid a crowd of bystanders and police. He had his trousers removed before being led away, and further footage appeared to show him with the T-shirt tied round his head talking to police.
The incident happened in a road that is partly blocked off with large concrete cubes that prevent direct access to streets adjoining the embassy.
Shortly afterwards there was an unusually heavy police presence with dozens of officers in the area.
Egypt has been fighting an insurgency led by Islamic State and concentrated in the Sinai Peninsula since the Egyptian military overthrew President Mohamed Mursi of the Muslim Brotherhood in mid-2013.