Turkey ? Police were interrogating four people detained after a bomb attack targeting Turkish soldiers in a passing bus killed five civilians and wounded 68 other people, a prosecutor said Friday.

A bomb-laden car exploded in the predominantly Kurdish city of Diyarbakir as a military service bus passed. The explosion set dozens of cars on fire and shattered the windows of buildings nearby, including one packed with students preparing for university entrance exams. Four of the dead were students, Durdu Kavak, chief prosecutor in the southeastern province, said in a written statement.

No one has claimed responsibility for the attack Thursday, but the Turkish leadership immediately blamed separatist Kurdish rebels.

A local official said the bombing was caused by some 88 pounds of plastic explosives. The official declined to be named because he was not allowed to speak with journalists.

Four people were being interrogated in Thursday’s attack, Kavak said.