A letter bomb exploded inside the car of former Greek Prime Minister Lucas Papademos in central Athens on Thursday, wounding him and two Bank of Greece employees, officials said.
All three were described as being conscious and hospitalized in stable condition.
"I unequivocally condemn the attack against Lucas Papademos," Prime Minister Alexis Tsipras tweeted from his official account. "I wish a speedy recovery to him and the people who accompanied him."
Police were on alert to determine whether any other parcel bombs might have been sent out, and were checking postal and courier services.
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.
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 haven't 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 hadn't yet been made, said the explosion occurred when Papademos opened an envelope inside the car. Anti-terrorism police were at the hospital where Papademos was being treated in order to interview him on the details of the envelope.
Another police official said one of the other two wounded in the blast told anti-terrorism police that he had handed Papademos the mail earlier, and that before doing so he had put it through an X-ray machine but that nothing suspicious had shown up.
The police official, who also spoke on condition of anonymity because no official announcement had been made, said the injured man said a book had been among the mail, and authorities were investigating whether the explosive device could have been inside that package.
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.
The group had also claimed responsibility for a spate of parcel bombings in 2010 targeting several embassies in Athens and the offices of European leaders abroad. Most of the devices were intercepted or destroyed by police, but one device injured a parcel company employee in Greece.
In the same year, a parcel bomb disguised as a gift exploded at the office of the Public Order Minister in Athens, killing one of the minister's top aides.
In Thursday's attack, police said Papademos' 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. Papademos' car bore little sign of damage, except for buckling on two doors.
The government described the blast as a terrorist attack.
"It is obvious and self-evident that the Greek government unreservedly and categorically condemns the attack against the former prime minister, Mr. Papademos," said government spokesman Dimitris Tzanakopoulos.
The spokesman said he had been given an update from doctors treating the wounded, who were "in a stable condition, are conscious, and are undergoing all the necessary medical tests so that their treatment can be determined."
Conservative opposition leader Kyriakos Mitsotakis, whose brother-in-law, conservative politician Pavlos Bakoyannis, was shot dead in 1989 by members of far-left terror group November 17, expressed "rage and pain" at the attack against Papademos.
"At some point we realize in this country that dealing with terrorism must take the highest priority. Terrorists are enemies of democracy," he said.
A respected economist, Papademos headed a provisional coalition government credited with preventing the collapse of the country's international bailout at the time. He also served as governor of the Bank of Greece between 1994 and 2002, when the country adopted the euro currency.