shut obey: Egypt's military gives politicians a 48-hour ultimatum

LIVE VIDEO ? Protesters gather in Tahrir Square in downtown Cairo, Egypt.

By Ayman Mohyeldin, Charlene Gubash and Ian Johnston, NBC News

CAIRO - Egypt?s military on Monday said mass protests calling for the resignation of Islamist President Mohammed Morsi were an ?unprecedented? expression of the will of the people and gave the government 48 hours to meet the opposition's demands.

In a statement read on state television just hours after the headquarters of Morsi?s Muslim Brotherhood movement were ransacked, General Abdel Fattah al-Sisi said if this did not happen the army would intervene.

The protesters' main demands are that Morsi announce early elections and step down, allowing a temporary government to take over.

"If the demands of the people are not realized within the defined period, it will be incumbent upon (the armed forces)... to announce a road map for the future,? the statement said. It was followed by patriotic music.

Protesters attacked and stormed the headquarters of the Muslim Brotherhood in Cairo, calling for Egypt's president Mohammed Morsi to step down. NBC's Ayman Mohyeldin reports.

The road map would be created by the army, which would also oversee the plan's implementation, the statement said.

It was unclear if the military was effectively demanding Morsi's resignation and a Muslim Brotherhood politician insisted there would not be "a coup."

On his Facebook page Monday, Morsi said he was meeting with the general al-Sisi as well as Prime Minister Hisham Kandil. What they discussed was not disclosed.

Sixteen people were killed and more than 700 were wounded during the protests Sunday and early Monday.

The military statement stressed that the military would remain neutral in politics and maintain its role as protector of the people and the nation?s borders.

The statement said the military will "not be a party in politics or rule."

But it added the armed forces had a responsibility to act because Egypt's national security was facing a "grave danger."

A source at Egypt's presidential palace said Morsi's office was not told in advance that the 48-hour ultimatum would be issued.

In Cairo's Tahrir Square, the vast crowd began to chant that the army and the people were one after al-Sisi's address. Army helicopters circled over the city flying Egyptian flags.

However, Yasser Hamza, a leader of the Brotherhood's Freedom and Justice Party,?warned against misinterpreting the army statement.?

"For an institution of state to come and stage a coup against the president, this will not happen," he said. "Any force that goes against the constitution is a call for sabotage and anarchy."?

In a formal response to Sisi's statement, an alliance of Islamist groups that includes Morsi's Brotherhood was careful not to criticize the army itself, instead saying that their political opponents were trying to manipulate the army to "assault legitimacy" in a way that would lead to a coup.

In a statement read at a press conference attended by a Reuters reporter, the alliance also said it respected all initiatives to resolve the country's political crisis, but that they had to respect constitutional principles.?

As the military statement was read, President Barack Obama urged all sides to refrain from violence shortly after he arrived in Tanzania.

"We're all concerned about what's happening in Egypt," Obama said. "There is more work to be done to create the conditions in which everybody feels that their voices are heard and that the government is responsive and truly representative."?

U.S. State Department spokesman Patrick Ventrell said the U.S. is closely watching the situation in Egypt, and is in touch with all sides, and?encouraged groups to avoid violence.

"Our message publicly and privately has been very consistent, that we want to see Egyptians succeed, that we don't take sides, we don't have a?particular party or group or interest that we're backing.? Ventrell said. ?Indeed, the only thing that we're backing is the Egyptian people and the goal?of their success in their democratic transition, that they can get their economy back on track, that they can fully see their democratic transition?succeed."

In a statement, the United Nation also called for Egyptians to resolve differences through ?democratic means.?

Five non-Brotherhood government ministers tendered their resignations from the Cabinet, apparently in sympathy with the protesters, underlining a sense of isolation for the party that won a series of elections last year but has failed to build out alliances to form a broader consensus.?

The attack on the Brotherhood building was bloodiest incident of the weekend's huge and mostly peaceful protests against Morsi.

It began after dark Sunday and continued for hours, with guards inside the suburban Cairo building firing on youths hurling fire bombs and rocks. Reuters cited medical and security sources as saying that eight people were killed but the figure could not be independently confirmed by NBC News.

Protesters breached ?the Cairo compound's defenses and stormed the building. Crowds later carried off furniture, files, rugs, air conditioning units and portraits of Morsi, according to an Associated Press journalist. One protester emerged with a pistol and handed it over to a policeman outside. ?

Footage on local television showed broken windows, blackened walls and smoke coming out of the building. A fire was still raging on one floor hours after the building was invaded. One protester tore down the Muslim Brotherhood sign from the building's front wall, while another hoisted Egypt's red, black and white flag out an upper-story window and waved it in the air in triumph.

Lasers were used as part of a demonstration in Cairo against President Mohamed Morsi. Hundreds of thousands of Egyptians flooded into the streets on the first anniversary of Morsi's inauguration on Sunday to demand that he resign.

The images were reminiscent of the destruction of the state security headquarters when Hosni Mubarak was toppled in 2011.

A spokesman for the Brotherhood said it would be demanding answers from security officials who failed to protect it. ?He said two of those inside were injured ?before a security detail from the movement was able to evacuate all those inside the compound in mid-morning.

Organizers behind Sunday's protests -- who managed to get 22 million signatures calling on Morsi to step down -- ?said they would give him until Tuesday at 5 p.m. (11 a.m. ET) to meet their demands otherwise they would call for nationwide strikes.?

Protesters also demanded?early elections, but late on Sunday night word from the presidential palace was that Morsi had no intentions of calling them.?

Some anti-Morsi protesters spent Sunday night in dozens of tents pitched in the capital's central Tahrir Square and in front of the president's Ittihadiya Palace. They have vowed to stay there until Morsi resigns. Morsi supporters, meanwhile, went on with their sit-in in front of a major mosque in Cairo.?

Sunday's protests were the largest seen in Egypt in the 2? years of turmoil since the ouster of autocratic Mubarak in February 2011.?

NBC News' F. Brinley Bruton, Jeff Black, Reuters and The Associated Press contributed to this report.