A bomb exploded inside the car of former Greek Prime Minister Lucas Papademos in central Athens, wounding him and two Bank of Greece employees, officials have said.
All three were described as being conscious and hospitalized in stable condition.
"We are all in shock following this action," said Nikos Pappas, a government minister and close aide to Prime Minister Alexis Tspiras.
"We condemn this appalling action without reservation and with all our heart wish Mr. Papademos the best."
Mr Papademos, 69, who served as prime minister for six months in 2011-2012 and is also a former deputy governor of the European Central Bank, had been inside his car when the device detonated.
Police have not officially confirmed reports that the blast was caused by a parcel bomb containing a small amount of explosives.
But a police official, speaking on condition of anonymity because an official announcement had not yet been made, said the explosion occurred when Mr Papademos opened an envelope inside the car.
Anti-terrorism police were at the hospital where Mr Papademos was being treated in order to interview him on the details of the envelope.
There was no immediate claim of responsibility for the attack, but Greek politicians have been targeted in the past by militant far-left and anarchist groups.
Earlier this year, a group called Conspiracy Cells of Fire, claimed responsibility for sending parcel bombs to the German Finance Ministry and the Paris office of the International Monetary Fund, where a small explosion injured one person.
Police said Mr Papademos's police escort had been in a car behind the former prime minister's vehicle, and that the other two wounded were Bank of Greece employees.
Authorities cordoned off the area, and forensics experts were investigating the scene for evidence.
The former prime minister's car was parked by the side of the road, in front of its escort vehicle. Mr Papademos's car bore little sign of damage, except for buckling on two doors.
Government spokesman Dimitris Tzanakopoulos called the blast an "attack" and said he had been given an update from doctors treating the wounded.
He said all were "in a stable condition, are conscious, and are undergoing all the necessary medical tests so that their treatment can be determined".
"With all out heart, we wish Mr Papademos and his companions a speedy recovery. The prime minister has been updated about all the events by the minister of public order and he will continue to receive updates," Mr Tzanakopoulos said.
A respected economist, Mr Papademos headed a provisional coalition government credited with preventing the collapse of the country's international bailout at the time.