A car packed with explosives detonated outside a security headquarters building in this city north of Cairo early Tuesday, killing 15 people and wounding more than 130 in one of the deadliest militant attacks in Egypt in years.

The powerful blast, which occurred just after 1 a.m. in a cramped quarter of Mansoura, was probably the work of a suicide bomber, Egypt's Interior Ministry said in a statement late Tuesday.

There was no immediate assertion of responsibility for the bombing, which killed 11 police officers and four civilians, according to state media. But the attack demonstrated the growing sophistication of Egypt's insurgency nearly six months after the ouster of Islamist President Mohammed Morsi in a military coup.