Police have appealed for passengers who used the Athens metro on Saturday afternoon to contact them if they saw something suspicious after revealing that someone left an incendiary device one a train.
The homemade device had been activated to explode but did not go off. It was placed in a green bag and left on the train that travelled between Ethniki Amyna and Egaleo stations at about 5 p.m.
The device was found at 5.18 p.m. on a seat at Egaleo ? the last station on Line 3 ? by the driver, who checked the carriages at the end of the journey.
Police are not sure whether the device was intended to go off while the carriage was carrying people or during the 10 minute wait before it headed in the other direction, towards Athens International Airport.
The device included a container with four liters of fuel, sources said. A technical fault meant that it failed to explode.
People with information that could relate to the incident have been asked to contact the anti-terrorism squad on 170, 1014 and 1964.
Authorities are examining CCTV footage and potential forensic evidence to see if they can obtain any information about the perpetrator or perpetrators.
No group has claimed responsibility for the device. Police sources said the device was similar to ones used by Conspiracy of the Cells of Fire in the past but almost all the suspected members of this urban guerrilla group have been arrested.
Although Greece has a long history of domestic terrorism, public transport has not been targeted before.