CAIRO -- Egypt's security authorities launched a sweep of arrests of Muslim Brotherhood members on Thursday, stepping up the government's confrontation with its top political nemesis.
The authorities warned that holding a leadership post in the group could now be grounds for the death penalty, as it has been officially declared a terrorist organization.
The announcement came as a bomb exploded in a busy Cairo intersection Thursday morning, hitting a bus and wounding five people. Though small, the blast raised fears a campaign of violence by Islamic militants that for months has targeted police and the military could turn to civilians in retaliation for the stepped up crackdown.
The terrorist labelling of the Brotherhood -- an unprecedented step even during past decades when the group was banned -- takes to a new level the government's moves to crush the group, which rode on elections to dominate Egypt's politics the past three years until the military removed Islamist President Mohammed Morsi in July after massive protests against him.
The Brotherhood vowed to "qualitatively" escalate its protests against the new military-backed interim government, whose authority it rejects. The group has struggled to bring numbers into the streets in past months under a crackdown that has already killed hundreds of its members and put thousands more in prison, including Morsi and other top leaders. There was little sign of protests Thursday.
The moves, playing out against a backdrop of increasing violence by al-Qaida-inspired militants, raise the potential for greater turmoil as the country nears a key Jan. 14-15 referendum on a revised constitution, a milestone in the post-Morsi political transition. The government is pushing for overwhelming passage of the new document and the Brotherhood vows to stop it with protests.
Ahmed Imam, a spokesman for the Strong Egypt Party founded by ex-Brotherhood member Abdel-Moneim Abolfotoh, warned the terrorism label "leaves the Muslim Brotherhood and its supporters only one choice, which is violence." Both sides are showing "a great deal of stupidity," he said, blaming the Brotherhood for failing to firmly distance itself from militant violence and the government for closing doors to reconciliation.
Speaking to military graduates Thursday, military chief Gen. Abdel-Fattah el-Sissi, who removed Morsi and is now Egypt's most powerful figure, vowed the country will "stand steadfast in confronting terrorism."
"Don't let any of the incidents happening now affect the will of Egyptians. Never," he said. "Anyone harms you will be wiped from the face of Earth."
Wednesday's terror designation means the Brotherhood's hundreds of thousands of members can be arrested for simple membership under a tough, years-old anti-terrorism law that outlines death penalties or long prison sentences for some crimes. The government says it will leave leeway for those who renounce the group's ideology and membership, but it didn't explain how, as members don't carry IDs to prove they belong.
The government said it urged other Arab governments to take similar steps under a 1998 regional anti-terrorism treaty to increase pressure on Brotherhood branches, especially in Gulf countries already known for longtime enmity to the group.
On Thursday, police arrested 16 Brotherhood members in the Nile Delta province of Sharqiya on charges of belonging to a terrorist group, the state news agency MENA said. Another 54 were arrested on accusations they attacked police stations or incited violence.
Private TV networks aired a hotline number for people to report "members of the terrorist Brotherhood" to the National Security Agency, raising the possibility of citizens turning on citizens and increasing the group's isolation.
Under the anti-terrorism law, those who participate in Brotherhood protests could face up to five years in prison, and "those leading this group (the Brotherhood) could be punished by the death penalty," he said.
In other steps, the Brotherhood's daily newspaper, Freedom and Justice, was suspended after security forces confiscated Thursday's edition.
To drain the group's resources, the government froze funds of more than 1,000 non-government organizations and charities linked to the Brotherhood and put more than 100 schools run by the group under government supervision.