Around 150 employees were evacuated from the building, in the 16th arrondissement, as a precaution and forensic officers were on site.
"I condemn this act of cowardly violence and reaffirm the IMF's resolution to follow through on its its work to ensure its mandate".
It is as yet unclear who sent the letter, which sounded like a "big firecracker" Cadot said, but authorities are investigating the incident.
"I have been informed about the explosion in the IMF's Paris office, which caused injuries to one of our staff".
France President Francois Hollande had said that the lethal attack was "clearly a terrorist assault".
Police say there have been telephone threats but it has not been made clear whether they were linked to the incident. The parcel was meant to be delivered to Finance Minister Wolfgang Schaeuble, and police indicated the device was engineered to inflict "severe injuries" when opened.
Many Greeks blame Germany and the International Monetary Fund for imposing years of public sector cuts and reforms in exchange for bailout packages needed to prop up the debt-ridden country. The package had Greek stamps on it and the return address was the address of a Greek MP, who did not send the package. Yet the first incident has sparked a manhunt by anti-terrorism investigators.