One person was injured on Thursday after an explosion at the International Monetary Fund (IMF) headquarters in Paris, security sources said.
The French media reported that the woman had opened a parcel addressed to a senior IMF official that contained an explosive substance, burning her hands and face.
Investigators told BFMTV the device was a "large black cylinder, about 30cm long", with the blast so large the room's ceiling was hit by shrapnel.
Police authorities in Paris said the explosive substance was not a bomb but rather a homemade "big firecracker", reported the Independent.
France's anti-terrorism branch has opened an investigation into attempted murder, destruction through explosive means, possession of explosive substance and links with a terrorist initiative, according to reports.
A spokesman for the police said the IMF office had received threatening phone calls in recent days but there was no evidence that they were linked to the incident.
IMF Director Christine Lagarde, who is on a trip to Germany, said in a statement she was informed about the explosion.
"I condemn this cowardly act of violence and reaffirm the IMF's resolve to continue our work in line with our mandate," she said.
Around 150 employees were evacuated from the building, in the 16th arrondissement, as a precaution and forensic officers were on site.
President Francois Hollande called the incident "an attack" and said those responsible will be found.
The blast came a day after a Greek anarchist group claimed responsibility for an explosive package found at the offices of Germany's Finance Minister Wolfgang Schauble.
"The package contained an explosive mix," Berlin Police said in a statement. "It was designed to cause severe injuries when the package is opened."
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