Greek former prime minister Lucas Papademos was hurt Thursday when an explosive device went off inside his car in Athens, state agencies said.
State news agency ANA said Papademos was undergoing surgery for abdominal and leg injuries at an Athens hospital.
State TV ERT earlier reported that he also had trouble breathing, but his life was not in danger.
Two of his guards were lightly hurt, ERT said.
"We are shocked. I wish to condemn this heinous act," media minister Nikos Pappas told the station.
ERT said Papademos, prime minister from 2011 to 2012, was wounded by a letter bomb as he read his post in the back of the car.
Prime Minister Alexis Tsipras, who is attending a NATO summit in Brussels, has been informed of the incident, ANA said.
A police source said a number of people had been hurt but could not say if Papademos himself was in the car at the time of the blast.
Papademos, 69, a former Bank of Greece governor, was in an armoured Mercedes provided by the bank, which contained the blast and likely aggravated his injuries, ERT said.
He headed an interim coalition government at the height of Greece's fiscal crisis that in 2012 negotiated a massive write-down of the country's privately-held debt.
He served as prime minister from November 2011 to May 2012 after the resignation of George Papandreou's socialist government, steering a batch of tough austerity measures through parliament before stepping down for elections to be held.
An economist by training, Papademos was Bank of Greece governor from 1994 to 2002, and European Central Bank governor vice president from 2002 to 2010.
There was no immediate claim of responsibility for the blast.
In March, Greek anarchist group Conspiracy of Fire Nuclei mailed a letter bomb that injured a secretary at the International Monetary Fund in Paris.
The Conspiracy of Fire Nuclei had earlier claimed responsibility for an explosive device, also sent from Greece, that was discovered by the police at the offices of German Finance Minister Wolfgang Schaeuble.
To make it more likely that the letter bombs would be opened, the attackers used the names of Greek politicians as alleged senders.
The group, which is considered a terror organisation by Washington, sent letter bombs to foreign embassies in Greece and to European leaders in 2010.