Egyptian Prime Minister Hazem Beblawi has declared the Muslim Brotherhood a "terrorist" organization.
Beblawi's spokesman made the announcement just hours after a car bomb exploded outside a police station in the city of Mansura, north of Cairo, on December 24.
At least 14 people were reported killed and more than 100 were injured in the blast, which caused the building to collapse.
The Muslim Brotherhood, however, issued a statement condemning the attack "in the strongest possible terms."
The prime minister's spokesman blamed the Muslim Brotherhood for the attack.
It came just one day after a group called Ansar Beit al-Maqdis said it considers Egyptian security forces to be "infidels" for obeying the country's secular, military-backed interim government.
Egyptian Interior Minister Mohammad Ibrahim, speaking on December 24 to Egypt TV after visiting the site of the blast in Mansura, said in a reference to the Muslim Brotherhood that security forces would bring to justice "the dark terrorist forces" trying to tamper with Egypt's stability.
"Just yesterday we arrested four activists who have confessed to some of these incidents, and they are now aware that we are taking measures against them," Ibrahim said. "And all of these incidents are an attempt to create a diversion and to terrorize people ahead of the [constitutional] referendum [scheduled for January 2014]. But I want to reassure people entirely that there is a plan in place in cooperation with the armed forces to protect all of the election centers at the highest level. And, God willing, the day will pass peacefully."
The Muslim Brotherhood has been blamed for many attacks targeting security forces since the army ousted Islamist President Muhammad Morsi in July.
Locals in Mansura have vented their anger at the group.
Shaimaa, a Mansura resident, blamed the Muslim Brotherhood for the bombing and urged the group to stop conducting violence around the country.
"All of this goes against God -- killing and destruction, and destroying people's lives," Shaimaa said. "It's been less than a week since [a taxi driver allegedly killed by the Muslim Brotherhood] was killed. Everyone is depressed, no one can sleep. We only want security. This goes against God, this is not Islam. This is not justice."
Based on reporting by dpa, AFP, and AP