The death toll in Egypt's Port Said has reached 26 as fighting raged following death sentences given to 21 people following a football riot last year.
"Twenty six people were killed and 277 injured," said Adbelrahman Farag, the head of Port Said hospitals.
Two policemen were among those killed, the interior ministry said, adding that there were "many critical injuries among police forces."
The clashes erupted after a Cairo court handed down the death sentence to 21 football fans and club members over the football riot last February in which 74 people were killed, and came a day after violence swept Egypt on the second anniversary of its uprising.
As news of the verdict emerged, relatives of those condemned tried to storm the prison in Port Said where they are being held, leading to fierce clashes with security forces.
Unidentified assailants used automatic weapons against police who responded with tear gas, witnesses said.
Two police stations in Port Said were stormed, an Agence France-Presse (AFP) correspondent said, and heavy gunfire could be heard in the Al-Manakh neighbourhood.
Ambulances ferried the injured to hospitals and all shops and businesses closed for the day as protesters set tyres alight and mosques urged worshippers to donate blood.
Troops are being sent to Port Said, a senior army officer said.
"It has been decided to deploy some units to work for calm and stability and the protection of public establishments," General Ahmed Wasfi said in a statement carried by the official MENA news agency.
Two policemen were among those killed, the interior ministry said in a separate statement, adding that there were "many critical injuries among police forces."
Egypt's opposition threatened to boycott upcoming parliamentary polls if President Mohamed Morsi – facing his worst crisis since coming to power in June – does not find a "comprehensive solution" to the unrest gripping the country.
The National Salvation Front, the main coalition of parties and movements opposing the ruling Islamists, called for, among other things, the creation of a "national salvation" government, otherwise it will "not participate in the next parliamentary elections."
'I am satisfied'
Last February's riots between fans of Port Said home side Al-Masry and Cairo's Al-Ahly also sparked days of violent protests in Cairo, in which another 16 people were killed.
In the capital, both inside and outside the court, there were explosions of joy at the verdict on Saturday. Women ululated, relatives hugged and shouted "Allahu Akbar" (God is greatest).
One man who lost his son in Port Said wept outside the court, telling AFP: "I am satisfied with the verdict."
Another, Hassan Mustafa, had pinned a picture of his dead friend to his chest and said he was pleased, but wanted "justice served for those who planned the killing."
Many Egyptians believe the violence was orchestrated either by the police or by supporters of ousted president Hosni Mubarak.
The Cairo court has handed its verdict to Egypt's top cleric for his final opinion, as is customary, and set March 9 for delivering verdicts on another 52 defendants, including police officers.
The sentence is subject to appeal, judicial sources said.
The sentences come after a day of clashes marking the revolution's second anniversary left at least nine people dead and 530 injured.
Tens of thousands took to the streets nationwide on Friday to protest against Morsi, who is accused of failing the revolution and consolidating power in the hands of his Muslim Brotherhood.
Egypt is also in the throes of an economic crisis as foreign investment and tourism revenues dwindle, the Egyptian pound stands at its lowest level against the dollar and a budget deficit shows no sign of reversing.
Morsi early Saturday used Twitter to appeal for calm, urging "citizens to adhere to the values of the revolution, express opinions freely and peacefully and renounce violence."
The interior ministry said 95 of its officers were injured on Friday, and Morsi said policemen were also among the dead. He expressed his condolences "to all Egyptians" over the deaths of both police and protesters.
Troops in armoured vehicles deployed in Suez late on Friday, taking up positions at the entry of the canal, outside police headquarters and the governorate building.
The canal authority said on Saturday shipping operations were unaffected by the violence.
Protesters also stormed government buildings in Ismailiya on Friday, and torched the Muslim Brotherhood headquarters.
In Cairo, police fired tear gas at protesters outside the presidential palace, where clashes between Morsi's allies and foes in December killed several people.
Protesters also set fire to tyres and blocked traffic on the 6 October bridge across the Nile, a flyover connecting east and west Cairo, and blocked the underground metro at several stations, paralysing public transport.
Demonstrators also clashed with the security forces in Egypt's second city Alexandria, witnesses said. – AFP.