PARIS, France (CNN) -- French officials are trying to determine who sent a parcel bomb that exploded Thursday in a Paris law office, killing a female assistant who opened the package.
A soldier stands in central Paris near where the parcel bomb exploded.
The blast seriously injured a lawyer standing nearby, but his injuries are not life-threatening, French Interior Minister Michele Alliot-Marie said
Speaking from the scene hours after the blast, Alliot-Marie said a courier delivered the "makeshift" letter bomb a short time before it detonated at approximately 12:50 p.m. (6:50 a.m. ET).
She said two explosive devices were inside the parcel -- one detonated and the other did not.
The package containing explosives was delivered to a fourth floor law office in a building on the Boulevard Malesherbes in Paris' 8th district, near the Champs-Elysees.
The office handles civil and commercial work, according to Paris prosecutor Jean-Claude Marin, who is participating in the investigation. It is unclear why it would be the target of an attack, Marin said.
He added it was unclear who the package was addressed to because of the extent of the damage.
Lawyer Christian Charriere-Bournazel told The Associated Press: "Someone came to the office and left a package. The secretary that opened it in fact opened a parcel bomb. The parcel bomb killed her."
Paris Mayor Bertrand Delanoe called it "a despicable act which must be condemned."
"It is my duty to first express my strongest condemnation of such a serious act, my compassion for the victim and her next of kin and for all the people who have been traumatized and shocked by such an act," he said.
The building contains several law offices, including the former firm of French President Nicolas Sarkozy, and an office for a foundation dedicated to the memory of the Holocaust, police said.
Serge Klarsfeld, a former Nazi war criminal hunter who is affiliated with the Holocaust foundation, told CNN he did not believe that office was the target of the attack.
A construction worker, who witnessed the aftermath, said a torrent of emergency workers descended upon the building.
"We were working on the building site and we heard the firemen and police sirens and they blocked the whole street," a construction worker told CNN affiliate, BFM TV.
"Then we saw a woman who came out wounded, covered in blood and who was hurting and she appeared to have a wound in her stomach and had blood on her legs. So they took her to a small store to take care of her, then we saw the bomb squad arrive who went inside the building to see what was going on and then the army arrived."
Hours after the blast, security was tight around the boulevard, which is lined with legal and financial offices. E-mail to a friend
CNN's Jim Bittermann in Paris and Pierre Meilhan in Atlanta contributed to this report