A letter exploded Thursday at the French office of the International Monetary Fund, slightly injuring one person, amid heightened security around Europe after a string of deadly attacks.
The incident came as a Greek anarchist group claimed responsibility for a failed letter bomb sent to the German Finance Ministry on Wednesday.
After Thursday's explosion in Paris, staff members at the IMF office were evacuated, and armed soldiers and police guarded the area, in a chic western district of the city.
It is unclear who sent the homemade explosive, which was like a "big firecracker" and sent by regular mail, said Paris Police Chief Michel Cadot. The IMF office had received threatening phone calls in recent days, but they were not necessarily linked to Thursday's incident, he said.
IMF Director Christine Lagarde, who is French, said in a statement that she was informed about the explosion while on a trip to Germany. "I condemn this cowardly act of violence and reaffirm the IMF's resolve to continue our work in line with our mandate," she said.
French President Francois Hollande, whose country remains in a state of emergency after the deaths of 235 people in Islamic extremist attacks over the last two years, told reporters Thursday in southern France: "We are again confronted with an attack. There is no other word for it when you are confronted with a package bomb."
Hollande later said the government would do "everything to find out the origin of this malicious act".
He said the letter bomb bore "a similarity with another event of the same nature in Berlin."
"We are trying to establish the causes of what happened as part of an international investigation," Hollande said.
The secretary who opened the letter was injured in the face by shrapnel and hurt in the eardrum because of a "rather violent noise," the police chief said.
Police searched all four floors of the building, which also houses the World Bank office in France, Cadot said. No one else was injured, and the building incurred only light damage.
The Greek group that claimed responsibility for the failed German letter bomb, Conspiracy of the Cells of Fire, said in an online posting Thursday on a Greek left-wing website that the attempted attack was part of a concerted campaign by international anarchist groups.
Many Greeks resent austerity measures imposed by the IMF and the European Union linked to Greece's bailout program.