A suicide bombing at a regional police headquarters in northern Egypt killed 15 people and injured more than 130 Tuesday, in an escalation of violence since the ouster of Islamist president Mohammed Morsi, dpa reported.
The government blamed Morsi's Muslim Brotherhood for the attack and said it was working to implement a court ban of the group. Prime Minister Hazem al-Beblawi vowed to respond with "force and decisiveness" to what he said was "the ugliest kind of terrorism".
The Interior Ministry said preliminary investigations showed the bomber drove a car laden with explosives through a checkpoint at the building in Mansoura, the capital of Dakahlyia province.
The bombing killed 12 policemen and injured Dakahlyia police chief General Sami al-Meihi.
The Health Ministry said the death toll climbed to 15 when a policeman died of his injuries and another had been found under the rubble by the evening.
Parts of the multistorey police headquarters collapsed, injuring passersby while windows in nearby buildings were shattered and several cars gutted in the explosion.
The presidency announced three days of mourning on Tuesday.
The government holds the Muslim Brotherhood and its Islamist allies responsible for the wave of unrest in the wake of Morsi's toppling by the army on July 3, after protesters called for him to step down.
In September, a court banned the group's activities and ordered the confiscation of its assets. Official and pro-government media have labelled the group as "terrorists."
Morsi, the country's first democratically elected leader, is facing a string of charges including that of conspiring with foreign militant groups.
Interior Minister Mohamed Ibrahim said the Muslim Brotherhood had carried out Tuesday's attack in retaliation for the violent dispersal by security forces of two Islamist protest camps in August.
"We are facing an enemy that has no religion or homeland, an enemy that does not care for people's lives and only seeks to destroy and destabilize the security of the state," Ibrahim said at the scene of the bombing.
The government's crackdown on Islamists has seen hundreds killed and thousands arrested.
The Muslim Brotherhood condemned the bombing and accused the government of aiming to create "further violence, chaos and instability."
"The Muslim Brotherhood considers this act as a direct attack on the unity of the Egyptian people and demands an inquiry, ... so that the perpetrators of this crime may be brought to justice," the group said.
In the wake of the bombing, thousands of people gathered in Mansoura, some 120 kilometres north of Cairo, to protest against the Brotherhood.
"The people want the execution of the Brotherhood," they chanted. Some protesters carried national flags and pictures of Defence Minister Abdel-Fattah al-Sissi, seen as the architect of Morsi's overthrow.
Morsi, who is being held at a prison in Alexandria, faces three trials on charges of sponsoring terrorism, conspiring with foreign organizations, inciting violence against protesters and escaping from prison during the 2011 uprising against his predecessor, Hosny Mubarak.
Hundreds of Islamists also face charges of inciting violence.
Protesters later performed funeral prayers for the victims. Shortly after, a mob attacked supporters of Morsi in the city who raised their hands with the four-finger sign that symbolizes people killed in the security crackdown.
They also set fire to a car belonging to a pro-Morsi resident, the state-run al-Ahram newspaper reported.
A supermarket believed to be owned by a brotherhood supporter was looted.
Security forces thwarted an attempt by "thugs who tried to storm the Mansoura central prison."
No group claimed responsibility for Tuesday's bombing, the worst attack so far outside the Sinai Peninsula and the Suez Canal area.
It came a day after a militant based in the Sinai Peninsula warned of strikes against the military. Ansar Beit al-Maqdis warned soldiers to leave the military or face death.
The group has claimed responsibility for the attempted assassination in September of the interior minister as well as several car bombings and attacks on security headquarters.