A powerful explosion has ripped through a police headquarters in an Egyptian Nile Delta city killing 13 people, wounding more than 100 and leaving victims buried under rubble in the deadliest bombing yet in a months-long wave of violence blamed on Islamic militants.
Investigators were trying to discover if the blast, soon after midnight in Mansoura, was from a car bomb or from explosives planted around the building. The explosion left a central street of the city strewn with piles of debris and charred cars.
Egypt has seen an escalating campaign of spectacular bombings and gun attacks, mainly against security forces, since the military removed Islamist president Mohammed Morsi in July and launched a fierce crackdown on his Muslim Brotherhood. Most have been centred in the Sinai Peninsula, where multiple militant groups operate, but the insurgency has been spreading to the heavily populated Delta and the capital, Cairo.
The interim government quickly blamed "dark terrorist forces" for the latest attack. A government spokesman went further and accused Morsi's Brotherhood of orchestrating the bombing and called it a "terrorist organisation."
Authorities appeared to be moving closer to officially declaring the Brotherhood a terrorist group. A court has already banned the group, but a terrorism designation would further escalate the crackdown against what was once the country's strongest political organization, winning elections the past three years and dominating the government during Mr Morsi's one year presidency.
The Brotherhood condemned the bombing as a "direct attack on the unity of the Egyptian people." It accused the government of "exploiting" the violence to target the group and "create further violence, chaos and instability."
Since the coup, carried out after massive nationwide protests demanding Mr Morsi's removal, Egypt's military-backed interim government has sought to portray the Brotherhood as largely responsible for the violence and militant attacks that engulfed the country following the 2011 overthrow of Hosni Mubarak.
Last week prosecutors referred Mr Morsi and other top Brotherhood leaders to trial on charges of organising a large terrorist conspiracy, working with Hamas, Hezbollah, Iran and other militant groups and orchestrating the Sinai insurgency in revenge for his removal.
The Brotherhood and its Islamist allies have been holding near daily protests demanding Mr Morsi's reinstatement, which often descend into clashes with security and anti-Brotherhood civilians. The protests have been met by a crushing crackdown that has killed hundreds of protesters and jailed thousands. At the same time, the army and security forces have been waging an offensive in Sinai against militant groups. Officials say more than 180 suspected militants and more than 170 policemen have been killed in violence the past months.
The attack on the police station in Mansoura, seen as a stronghold of Brotherhood support, was the first major bombing in the Nile Delta.
The blast struck at the security headquarters, collapsing an entire section and side wall of the five-floor building. Dozens of parked cars were incinerated, and several nearby buildings were damaged, including a bank and theatre.
The dead included nine policemen, and 101 people were wounded, among them the city's security chief - who lost an eye - and his assistant.
Egypt's Interior Minister Mohammed Ibrahim toured the scene of the explosion at daybreak, pledging that the police will "continue their battle against the dark terrorist forces that tried to tamper with the country's security," then went to hospital to visit the wounded.
Egypt's turmoil comes as the country nears a January 14-15 referendum on a revised constitution, a key step in a military-backed transition plan leading to presidential and parliamentarian elections later next year. Mr Morsi's supporters bitterly oppose the new document, which amends the constitution passed under his rule.