CAIRO (CNN) -- A day after ferocious clashes left more than 500 people dead in Egypt, four more people were killed in clashes in Alexandria, state media reported. Elsewhere, protesters stormed a government building in Giza and blocked a road near the nation's iconic pyramids.

State-run Nile TV reported the Alexandria deaths occurred in fighting between Muslim Brotherhood members and residents of the city.

Earlier Thursday, the Giza Governate building was evacuated after supporters of ousted President Mohamed Morsy stormed the building, Nile TV reported. Televised images later showed the building on fire. Nile TV also said protesters had blocked a road near the pyramids while others staged a sit-in at a mosque in Nasr City. It was unclear if anyone had been injured.

State-run TV also said Morsy supporters were attacking police stations, hospitals and government buildings in areas outside Cairo, despite a state of emergency declared Wednesday by the military-backed interim government which limits public gatherings and gives more power to security forces to make arrests.

In Cairo, meanwhile, an eerie and tense calm prevailed Thursday, one day after hundreds died in violence sparked when security forces moved in to clear two camps of Morsy supporters. Traffic on the city's normally teeming streets was light amid fears of further fighting.

The Muslim Brotherhood vowed Thursday that protests would go on, despite violence Wednesday that brought international criticism of Egypt's interim government.

"We will continue our sit-ins and demonstrations all over the country until democracy and the legitimate rule are restored in Egypt," said Essam Elerian, a senior member of the Islamist movement.

Egypt's short-lived experiment with democracy took a gruesome turn Wednesday, culminating in mass carnage and a return to the repressive state of emergency that had gripped the country for 30 years.

The Egyptian Health Ministry said at least 525 people died and more than 3,700 were injured Wednesday in clashes that began when security forces moved in to break up protesters demonstrating in support of Morsy. Among the dead were 43 police officers, the interior ministry said.

The death toll could rise. On Thursday, Muslim Brotherhood officials displayed at least 100 bodies, wrapped in white, blood-stained sheets, at the Emam Mosque in Cairo, some of the 500 people the group said were brought to the mosque after the violence.

The Muslim Brotherhood and other activists on the ground told CNN those bodies had not yet been registered with authorities.

While Egypt's interim government said the violence began after protesters violently resisted their peaceful efforts to disperse pro-Morsy sit-ins, demonstrators said security forces had staged a "full-on assault."

CNN journalists on the ground said many of those injured or killed were unarmed. It was Egypt's bloodiest day since the 2011 revolution to oust Morsy's predecessor, Hosni Mubarak.

The shocking violence brought criticism from countries around the world and threatened to further destabilize Egypt's already precarious economy and political situation.

On Thursday, U.S. President Barack Obama strongly condemned the bloodshed, saying the government chose violence and arbitrary arrests over an opportunity to resolve its crisis through peaceful dialogue.

"The United States strongly condemns the steps that have been taken by Egypt's interim government and security forces," Obama said in a statement from his summer vacation home. "We deplore violence against civilians."

He urged the government to lift the state of emergency imposed Wednesday and to launch a reconciliation process immediately.

He also canceled joint U.S.-Egyptian military training exercises scheduled next month, and warned that the traditional cooperation between the two nations "cannot continue as usual when civilians are being killed in the streets."

His comments came a day after Secretary of State John Kerry said the crackdown was "a serious blow to reconciliation and the Egyptian people's hopes for a transition towards democracy and inclusion."

Denmark suspended economic aid to the country. China urged restraint. Germany, Italy, France and other nations summoned Egypt's ambassadors to their nations to express dismay over the violence.

The raid

Security forces raided the pro-Morsy camps Wednesday after weeks of simmering tension. Clashes and gunfire broke out, leaving pools of blood and bodies strewn all over the streets.

Authorities bulldozed tents and escorted hundreds of people away. Some mothers and fathers managed to whisk away their children, gas masks on their faces.

The dead included cameraman Mick Deane, who'd worked for UK-based news channel Sky News for 15 years and for CNN before that.

Morsy supporters also reportedly attacked a number of Christian churches. It's not clear how many were targeted, but Dalia Ziada, of the Ibn Khadun Center for Development Studies, said Thursday that the center had documented the burning of 29 churches and Coptic facilities across the country.

"This is horrible to happen in only one day," she said.

The Bible Society of Egypt said 15 churches and three Christian schools had been attacked, some set on fire.

At least 84 people, including Muslim Brotherhood members, have been referred to military prosecutors for charges including murder and the burning of churches, the state-run EGYNews site reported.

But protesters vowed to remain defiant until Morsy is reinstated.

Elerian, the senior Muslim Brotherhood member, said he's not deterred by calls for his arrest.

"They can arrest me and 100 of us, but they can't arrest every honorable citizen in Egypt," Elerian told CNN Thursday. "They can't stop this glorious revolution."

The government's state of emergency declaration mirrors the kind of stifling police state that the nation lived through under Mubarak, before the Egyptian people rose up in protests that resulted in Mubarak's overthrow in 2011 and eventually Morsy's rise to power as the country's first democratically elected president.

Morsy's rise, fall

But rather than uniting Egypt after Mubarak's fall, divisions intensified during Morsy's time as president.

Critics accused him of being authoritarian, trying to force the Muslim Brotherhood's Islamic agenda on the country and failing to deliver freedom and justice.

Morsy's supporters say the deposed president wasn't given a fair chance, and say his backers have been unfairly targeted for expressing their opinion.

Though Morsy has not appeared in public since he was taken into custody, his supporters have amassed on the streets nationwide to slam military leaders and demand his reinstatement.

More setback

Even Egypt's interim government suffered a major setback after the raid.

Mohammed ElBaradei -- a secular leader who was one of Morsy's biggest critics -- submitted his resignation Wednesday as vice president.

ElBaradei said he didn't agree with the decisions carried out by the ruling government and "cannot be responsible for a single (drop of) blood."

CNN's Reza Sayah reported from Cairo; Michael Pearson wrote from Atlanta. CNN's Ian Lee, Frederik Pleitgen, Laura Smith-Spark and Holly Yan also contributed to this report.