At least five people have been killed and 265 others arrested as Egyptian riot police deployed water cannon and tear gas against hundreds of rock-throwing supporters of former president Mohamed Morsi, government officials said.

The clashes on Friday followed an announcement by Egyptian authorities that they would use the Muslim Brotherhood's new designation as a terrorist organisation to levy harsh prison sentences on protesters.

"Brotherhood actions caused the deaths of [several] citizens when they clashed with residents," the Interior Ministry said in a statement on the violence, which gripped several cities.

Authorities, meanwhile, unveiled a new tactic to contain protests called by Morsi's Muslim Brotherhood group and its allies, calling on large families to post armed men near the likely sites of demonstrations.

A 20-year-old protester was shot and killed in Damietta province, while another protester was killed in Menia when a tear gas canister struck him in the face. A third protester was killed in Cairo, according to the Health Ministry.

Al Jazeera sources say an elderly man died from inhaling tear gas, and two police cars were set ablaze when anti-coup protesters clashed with police in Aswan. Police also fired tear gas and birdshot at protesters at al-Azhar University in Cairo's northern district of Nasr City.

The protests at al-Azhar were fuelled by the death of a student at the historic seat of Sunni Muslim learning late on Thursday, as protesters defied a law issued by the government on Wednesday labelling the Muslim Brotherhood a terrorist group.

Vow to continue

The Interior Ministry said 15 policemen were injured in nationwide clashes with anti-coup protesters after being shot with live ammunition or birdshot.

Police and protesters also clashed in the Suez Canal city of Ismailia, where gunfire was heard, and in Damietta, in the Nile Delta, after Friday prayers.

The Muslim Brotherhood has vowed to keep up their protests, despite the arrests.

"Let's begin with full force and peacefulness a new wave of majestic anti-coup action," the Brotherhood-led Anti-Coup Alliance said in a statement on Friday.

More than 20 Muslim Brotherhood supporters were also arrested on Thursday on accusations of belonging to and passing out leaflets in support of the movement, according to Egypt's state media agency, MENA.

Anyone accused of taking part in pro-Muslim Brotherhood rallies, possessing the group's literature, or supporting the group "verbally or in writing" could be sentenced to five years in prison, the Interior Ministry said.

Deadly blast

A months-long clampdown against the Islamist group, which has won every vote since the 2011 uprising toppling former President Hosni Mubarak, was upped after a Tuesday blast in the Nile Delta city of Mansoura ripped through a police station and killed 14 people.

Egyptian army chief General Abdel Fattah el-Sisi, who led the July 3 military coup following mass protests against Morsi, vowed to wipe off earth "those who hurt Egyptians".

His pledges were renewed after another bomb on Thursday injured five people near al-Azhar.

"Egypt will stand firmly in confronting terrorism and the people will never be afraid as long as the army is present," he said during an army graduation ceremony on Thursday in Cairo.

The Muslim Brotherhood was blamed for Tuesday's attack, although an al-Qaeda-inspired group known as Ansar Bayt al-Makdis claimed responsibility.

No party has claimed responsibility for Thursday's bomb.