An explosion early Sunday damaged the door and some windows of a business school that had been headed by a man recently appointed France's first prefect of Muslim origin -- whose car was bombed a week ago.

Police immediately cordoned off the area around the Audencia (search) school and opened an investigation.

Aissa Dermouche (search), 57, born in Algeria, was named to the prestigious post of prefect, the state's highest representative of a region, on Jan. 14 by President Jacques Chirac (search).

Four days later, his car, parked on a street near his home, was blown up.

Dermouche's appointment was a major event in France, which is struggling to integrate its Muslim citizens, a population estimated at some 5 million -- the largest in Western Europe.

Investigators are still trying to ascertain who blew up Dermouche's car. They explored the possibility of personal revenge, detaining three people connected to Dermouche's ex-wife. However, the three were released on Thursday.

Sunday's 6:15 a.m. blast damaged the door and broke some windows at the Audencia school.

Ziad Khoury, a deputy prefect of the Loire Atlantique, the western France region where Nantes is located, said that there apparently were no witnesses to the explosion at Audencia, a well-known business school headed by Dermouche until he was named a prefect.