The controlled detonation of an American World War II bomb in the southern German city of Regensburg has still caused widespread damage to nearby houses.

Some 4,500 residents had to be evacuated from the area before experts performed the detonation. A spokeswoman for the Bavarian city, Dagmar Obermeier-Kundel, said the 250-kilogram (550-pound) bomb still shattered windows in several surrounding buildings early Wednesday. Photos also showed damaged roofs.

Munitions expert Andreas Heil told The Associated Press that the bomb couldn't be safely defused because the type of detonator it contained was tamper-proof, very sensitive and could have triggered an explosion at any moment.

Thousands of unexploded relics of World War II's extensive aerial bombardment are found in Germany every year, even 74 years after the end of the war.