Updated 9:36 p.m. ET
CAIRO With the clock ticking, Egypt's besieged president said Tuesday that he will not step down as state media reported that the powerful military plans to overturn his Islamist-dominated government if the elected leader doesn't meet the demands of the millions of protesters calling for his ouster.
Mohammed Morsi's defiant statement sets up a major confrontation between supporters of the president and Egyptians angry over what they see as his efforts to impose control by his Muslim Brotherhood as well as his failure to introduce reforms more than two years after the revolution that ousted his autocratic predecessor Hosni Mubarak.
Writing Tuesday on his official Twitter account, Morsi said he "asserts his adherence to constitutional legitimacy and rejects any attempt to breach it and calls on the armed forces to withdraw their ultimatum and rejects any domestic or foreign dictates." He then went on Egyptian television to deliver a public address, vowing to protect democratic "legitimacy" with his life.
Morsi accused loyalists of his predecessor Hosni Mubarak of riding the current wave of protests to topple his regime. "There is no substitute for legitimacy," he said.
The leaking of the military's so-called political road map appeared aimed at adding pressure on Morsi by showing the public and the international community that the military has a plan that does not involve a coup.
Political violence was more widespread on Tuesday, with multiple clashes between the two camps in Cairo as well as in the Mediterranean city of Alexandria and other cities. A march by Morsi supporters outside Cairo University came under fire from gunmen on nearby rooftops.
At least 10 people were killed in Cairo and more than 70 injured, according to hospital and security officials who spoke on condition of anonymity because they were not authorized to talk to the media.
Protesters also turned to a new target Tuesday, massing a giant crowd outside the Qasr el-Qobba presidential palace where Morsi has been working in recent days, in addition to filling wide avenues outside another palace, central Tahrir Square and main squares in cities nationwide.
Morsi's supporters increased their presence in the streets, after his Muslim Brotherhood and hard-line Islamist leaders called them out to defend the legitimacy of the country's first freely elected president. Tens of thousands held marches in Cairo and other cities. Clashes broke out around pro-Morsi marches in several parts of the capital and a string of cities to the north and south. Morsi opponents stormed Brotherhood offices in two towns.
Gehad al-Haddad, a senior Muslim Brotherhood spokesman, told CBS News' Alex Ortiz the military's threat has changed the game.
"I think it's a coup," al-Haddad said.
Al-Haddad called the threat "completely unacceptable," but added that his organization will not be caught off-guard if the military makes good on its threat.
"We are shifting our tactics," al-Haddad said. "We have had a scenario for this for some time. If military moves on the ground we have a plan for that."
While the army has refused to call their plans a coup, CBS News correspondent Clarissa Ward reports, retired Gen. Sameh Elyazal was clear about the need for immediate change.Elyazal told Ward that technically, Morsi has the right to finish his term because he was democratically elected. "But you want me to wait until we see our country completely collapsed?" he said. "In the first year, he did many mistakes. Look at the economy in Egypt. I am running with my pistol in my back, why, because the streets of Egypt are not safe.
Fearing an implosion that could throw Egypt into chaos, U.S. officials said Washington has suggested to Morsi that he call early elections, though they underlined they were demanding specific steps - and they said they had underlined to Egypt's military that a coup would have consequences for U.S. aid. The officials spoke on condition of anonymity because they were not authorized to speak publicly about the matter.
Morsi adviser Ayman Ali denied that Washington asked the president to call for early presidential elections and said consultations were continuing to reach national conciliation and resolve the current political crisis. He did not elaborate.
The army has underlined that it has no intention to take power. But the reported army road map showed it was ready to replace Morsi and make a sweeping change in the ramshackle political structure that has evolved since the 2011 fall of autocrat Hosni Mubarak.
A retired army general with close ties to the military confirmed the news agency report on the road map.
Hossam Sweilam said a panel of experts would draft a new constitution and the interim administration would be a presidential council led by the Supreme Constitutional Court's chief justice and including the defense minister, representatives of political parties, youth groups, Al-Azhar Mosque and the Coptic Church.
He said the military envisaged a one-year transitional period before presidential elections are held.
The military spokesman, Col. Ahmed Mohammed Ali, declined to confirm the details. "It is too early and we don't want to jump into conclusions," he said.
In a significant move, opposition parties and the youth movement behind the demonstrations agreed that reform leader and Nobel Peace laureate Mohamed ElBaradei would represent them in any negotiations on the country's political future. The move appeared aimed at presenting a unified voice in a post-Morsi system, given the widespread criticism that the opposition has been too fragmented to present an alternative to the Islamists.
Morsi faced fissures from within.
Three government spokesmen -- two who spoke for Morsi and one who spoke for Prime Minister Hesham Kandil - were the latest to quit as part of high-level defections that underscored his increasing isolation and fallout from the military's ultimatum. Five Cabinet ministers, including the foreign minister, resigned Monday, and sixth, Youth Minister El-Amry Farouq, quit Tuesday.