Hundreds of supporters of Egypt's deposed President Mohamed Morsi took to the streets Thursday to protest deadly security crackdowns on their sit-ins the day before.
The Muslim Brotherhood called on its supporters to hit the streets in spite of the state of emergency imposed by the army-backed interim government to curtail the violence, which left at least 638 people dead and 3994 injured, according to Egyptian Health Ministry spokesperson Mohammed Fathallah.
Protesters stormed a government building in Giza, a city neighboring Cairo, throwing Molotov cocktails that set the building on fire, Interior Ministry sources told Al Jazeera.
Brotherhood spokesman Gehad El-Haddad said anger within the 85-year-old Islamist movement, which has millions of supporters across Egypt, was "beyond control."
Supporters of the Brotherhood, which is Egypt's largest political organization and is demanding Morsi's reinstatement, are also marching in Egypt's second largest city of Alexandria, where hundreds of mourners attended a funeral procession for a police officer who was killed during Wednesday's clashes.
VIDEO: Bullets fly on Cairo streets
Meanwhile, in response to the violent crackdown, President Barack Obama said in a press conference Thursday that the U.S. is canceling a bi-annual joint military exercise with Egypt scheduled for next month.
Obama said the U.S. "strongly condemns" violent steps taken by the state security forces, and called for the state of emergency to be lifted.
"We sustain our commitment to Egypt and its people ... but our traditional cooperation cannot continue as usual," the president said, announcing the cancellation of the Bright Star exercises, which typically involve several other European and Arab allies.
However, Obama did not mention any changes to the $1.3bn annual U.S. military aid package to Egypt.
Late Thursday, the military-backed interim Egyptian government released a statement saying that Obama's remarks were not based on "facts" and would only strengthen and encourage violent opposition.
Also Thursday, Egyptian authorities authorized police to use deadly force and ammunition in dealing with attacks on government buildings and police forces, the Interior Ministry said in a statement Thursday, prompting members of the U.N. Security Council to request an emergency meeting late afternoon to discuss the voltaile situation in the country.
Security sources said that the police had arrested Mostafa Hamza, a council leader in the radical armed militant group Gamaa Islamiya, for joining the pro-Morsi sit-in in Rabaa. The group is seen as more extreme than the Brotherhood.
Elsewhere, four Egyptian soldiers were shot dead by unknown gunmen near the city of el Arish in the North Sinai region, security and medical sources said.
TIMELINE: EGYPT IN TURMOIL
The interim government, which imposed a month-long, nationwide state of emergency in Cairo and 13 other provinces after the violence Wednesday, said it was determined to confront "terrorist acts" by Muslim Brotherhood members.
Egyptian authorities also referred 84 people -- including members of the Muslim Brotherhood -- from the coastal city of Suez to military prosecutors on charges of murder and burning of churches, state news agency MENA reported. Morsi's detention has been extended for another 30 days as the ruling military continues its crackdown on the Brotherhood.
Muslim Brotherhood spokesman Gehad El-Haddad said on Twitter that its supporters would remain peaceful in their attempts to reverse the July 3 military coup that ousted Morsi.
But later, El-Haddad said the Anti-Coup Alliance, an umbrella group opposed to Morsi’s ouster, suffered a "very strong blow" in the violent military crackdown. "After the blows and arrests and killings that we are facing, emotions are too high to be guided by anyone," he said.
Graphic photographs and video of the Cairo bloodbath dominated social media networks, as world powers called for restraint and condemned the show of force by security forces.
Al Jazeera's Jane Ferguson, reporting from al-Iman Mosque in Cairo close to Rabaa al Adawiya Square, where more than 200 people were killed, said the scene is "absolutely horrific" as funerals begin.
"The bodies all across the floor surrounded by bloody shrouds. Lots of relatives crying, lots of anger," she said. "We have seen coffins being brought steady stream in here now. There are already 100 bodies behind me."
The Gulf News newspaper reported on its website that a subsidiary publication's correspondent, Habiba Ahmed Abd Elaziz, 26, was killed near the Rabaa al Adawiya mosque. Egyptian journalist Ahmed Abdel Gawad also lost his life as security forces moved in. Britain's Sky News said a veteran cameraman, Mick Deane of th U.K., was shot and killed while covering the assaults.
The violence in Egypt has triggered protests in other countries.
Small rallies were held in the Israeli capital Tel Aviv, and in Gaza in support of the pro-Morsi groups cleared by Egyptian security forces. There were also demonstrations in Turkey, Tunisia and Jordan.
The Rafah border crossing between Egypt's Sinai and Gaza has been closed indefinitely, leaving hundreds of Palestinian travelers stranded.
At least four churches in Egypt were attacked, with Christian activists accusing Morsi loyalists of waging "a war of retaliation against Copts in Egypt." Coptic Christians make up about 10 percent of Egypt's predominantly Muslim population.
Among those killed in Cairo was 17-year-old Asmaa al Beltagi, daughter of wanted Brotherhood leader Mohammed al Beltagi, a spokesman for the organization said.
The violence prompted vice president and Nobel Peace Prize laureate Mohamed ElBaradei to resign, saying his conscience was troubled over the loss of life, "particularly as I believe it could have been avoided."
"It has become too difficult to continue bearing responsibility for decisions I do not agree with and whose consequences I fear," he said.
Wednesday's crackdown came hours after the United States had urged the government to allow Morsi supporters to protest freely. White House Deputy Press Secretary Josh Earnest said that the Obama administration condemns violence against Egyptian protesters, and that the crackdown makes the "path to stability harder."
Morsi became Egypt's first freely elected leader in June 2012, but a deepening economic malaise and fears over autocratic Islamist rule brought hundreds of thousands of Egyptians into the streets earlier this summer to demand his ouster.
Al Jazeera and wire services