A Japanese man set a car on fire at the entrance to the country's lower house of parliament on Thursday.
Japanese media said the driver, who is now in police custody, claimed to belong to a right-wing group.
Initial reports said he had crashed the car into a gate near the building, but later reports suggested he had parked and purposely set the vehicle alight.
Security has been tightened around the parliament building since Japan agreed to send non-combat troops to Iraq.
Television footage showed black smoke billowing from the burning vehicle.
Three fire engines rushed to the scene soon after the incident, and the flames were quickly extinguished.
The driver has reportedly claimed to be a former right-wing extremist.
According to Kyodo news agency, he was angry at the Japanese government's failure to make headway in talks with North Korea over Japanese citizens abducted by Pyongyang decades ago.