At least 149 Egyptians were killed on Wednesday after security forces moved in on protesters demanding the reinstatement of President Mohammed Morsi, and the government imposed a state of emergency as unrest swept the most populous Arab nation.

Troops opened fire on demonstrators in violence that brought chaos to areas of the capital and looked certain to further polarize Egypt's 84 million people between those who backed Morsi and the millions who opposed his brief rule.

The state of emergency, starting at 2:00 P.M. on Wednesday, was to last a month.

According to a Health Ministry official, quoted on the official MENA news agency, some 1,403 were wounded.

Egypt's interim vice president, Mohamed ElBaradei, resigned after the protest crackdown.

In a resignation letter to Interim President Adly Mansour, ElBaradei said that "the beneficiaries of what happened today are those who call for violence, terrorism and the most extreme groups," he said. "It has become difficult for me to continue bearing responsibility for decisions that I do not agree with and whose consequences I fear. I cannot bear the responsibility for one drop of blood."

In the streets around the Rabaa al-Adawiya mosque in northeast Cairo, where thousands of Morsi supporters have staged a sit-in for the last six weeks, riot police wearing gas masks crouched behind armored vehicles, tear gas hung in the air and burning tires sent plumes of black smoke into the sky.

The White House condemned the violent crackdown on protesters in Egypt on Wednesday and strongly opposed the declaration of a state of emergency made by Egypt's military leaders.

Obama was briefed about the killing of at least 95 Egyptians and was being kept up to date on the situation by his national security adviser, Susan Rice. With death tolls ranging from 95 to 800, White House spokesman Josh Earnest said U.S. officials were seeking clarification.

"We have repeatedly called on the Egyptian military and security forces to show restraint, and for the government to respect the universal rights of its citizens, just as we have urged protesters to demonstrate peacefully," said Obama.

White House spokesman Josh Earnest gave no indication that the United States is prepared to immediately cut off billions of dollars in military assistance to Egypt. He did say, however, that U.S. aid to Egypt is under review, as it has been for weeks.

"The world is watching what is happening in Cairo. We urge the government of Egypt - and all parties in Egypt - to refrain from violence and resolve their differences peacefully," said Earnest.

In response to Egypt's actions, Turkey urged the UN Security Council and Arab League on Wednesday to act quickly to stop a "massacre" in Egypt, and Iran warned of the risk of civil war, after Egyptian security forces killed dozens of Islamist demonstrators.

European leaders also criticized the violence against a camp of protesters seeking the restoration of deposed Islamist President Mohamed Morsi, calling for restraint and a return to meaningful dialogue to defuse Egypt's political stand-off. "The reports of deaths and injuries are extremely worrying," Michael Mann, a spokesman for EU foreign policy chief Catherine Ashton said. "We reiterate that violence won't lead to any solution and we urge the Egyptian authorities to proceed with utmost restraint."

Turkish President Tayyip Erdogan said international passivity had paved the way for the military-backed Egyptian government's crackdown, which included violence in areas beyond the capital that killed at least 14 protesters.

"It is clear that the international community, by supporting the military coup (that ousted Morsi on July 3), and remaining silent over previous massacres instead of protecting democracy and constitutional legitimacy in Egypt, has encouraged the current administration to carry out today's intervention.

"The international community, especially the UN Security Council and Arab League, must act immediately to stop this massacre," Erdogan, whose government is Islamist-rooted, said in a statement.

UN Secretary General Ban Ki-moon on Wednesday condemned violence used by Egyptian security forces to clear Cairo of protesters demanding the reinstatement of deposed President Mohamed Morsi.

While the United Nations was still gathering information, it appeared that hundreds of people were killed or wounded in clashes between security forces and demonstrators, according to a statement by the secretary-general's spokesperson.

At a hospital morgue in Cairo, a Reuters reporter counted 29 bodies, including that of a 12-year-old boy. Most had died of gunshot wounds to the head. A nurse at the same hospital had said she counted 60 bodies, and expected the number to rise.

Also, a Sky News cameraman was shot and killed while covering the Egyptian response to the protests. Sixty-one-year-old Mick Deane was a Sky News cameraman for fifteen years, based primarily in the Middle East.

The unrest spread beyond the capital, with the cities of Minya and Assiut, and Alexandria on the northern coast, also affected. Seventeen people were killed in the province of Fayoum south of Cairo. Five more died in Suez.

Mohamed El-Beltagi, a leader of Morsi's Muslim Brotherhood movement that led the protests, warned of wider conflict and singled out the head of the armed forces who deposed Morsi on July 3 following mass protests that called for his resignation.

"I swear by God that if you stay in your homes, Abdel Fattah Al-Sisi will embroil this country so that it becomes Syria. Abdel Fattah Al-Sisi will push this nation to a civil war so that he escapes the gallows."

Nine hours after the start of the operation, crowds of protesters were still blocking roads, chanting and waving flags as security forces sought to prevent them from regrouping.

"At 7 a.m. they came. Helicopters from the top and bulldozers from below. They smashed through our walls. Police and soldiers, they fired tear gas at children," said teacher Saleh Abdulaziz, 39, clutching a bleeding wound on his head.

"They continued to fire at protesters even when we begged them to stop.The West, notably the United States which gives the Egyptian military e1.3 billion each year, has been alarmed by the recent violence in the strategic Arab ally that has a peace treaty with Israel and controls the vital Suez Canal waterway.