Cairo - Egypt's military has drawn up a plan to suspend the Islamist-backed constitution, dissolve the Islamist-dominated legislature and set up an interim administration headed by the country's chief justice if President Mohammed Morsi fails to reach a solution with his opponents by the end of a Wednesday deadline, the state news agency reported.
The report on Tuesday provided the first details on the road map that the military has said it will implement if Morsi fails to meet its ultimatum, as millions of protesters returned to the streets for the third straight day in their drive to force the Islamist president out of office.
The president's Islamist backers have stepped up warnings that it will take bloodshed to dislodge him, saying they would rather die fighting a military takeover than accept Morsi's ousting just a year after the country's first free election.
"Seeking martyrdom to prevent the ongoing coup is what we can offer as a sign of gratitude to previous martyrs who died in the revolution," Brotherhood stalwart Mohammed el-Beltagi wrote on Tuesday in his official Facebook page.
Protesters turned to a new target, massing a giant crowd outside Cairo's Qasr el-Qobba presidential palace where Morsi has been working in recent days - though he was not believed to be inside - in addition to filling wide avenues outside another palace, central Tahrir Square and main squares in cities nationwide.
Morsi's supporters also increased their presence in the streets, after his Muslim Brotherhood and hard-line Islamist leaders called them out to defend what they say is the legitimacy of the country's first freely elected president. Tens of thousands held marches in Cairo and other cities.
With the clock ticking on the military's ultimatum, many in the anti-Morsi and pro-Morsi camps were vowing to fight to the end.
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. At least 16 have been killed since Sunday in clashes, most of them anti-Morsi protesters shot to death by Islamists.
Fearing an implosion that could throw Egypt into chaos, US 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 US aid.
The officials spoke on condition of anonymity because they were not authorised 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.
Morsi met with the army's chief, Defence Minister Gen Abdel Fattah el-Sisi, and Prime Minister Hesham Kandil in the second such meeting in as many days, Ali said, without giving details.
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.
The report's leaking also appeared aimed at adding pressure to Morsi by showing the public - and the Americans - that the military has a plan that does not involve its direct rule.
The constitution and domination of the legislature after elections held in late 2011-early 2012 are two of the Islamists' and Brotherhood's most valued victories - along with Morsi's election last year.
A retired army general with close ties to the military confirmed the news agency report's version of 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 defence 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 spokesperson, Colonel Ahmed Mohammed Ali, declined to confirm the details. "It is too early and we don't want to jump into conclusions," he said.
At least one anti-Morsi TV station put up a clock counting down to the end of the military's ultimatum, putting it at 16:00 on Wednesday (14:00 GMT), though a countdown clock posted online by Morsi opponents put the deadline at 17:00 (15:00 GMT). The military did not give a precise hour.
Morsi faced new fissures within his leadership.
Three government spokespeople - two for Morsi and one for the prime minister - 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 on Monday, and sixth, Sports Minister El-Amry Farouq, quit on Tuesday.
One ultraconservative Salafi party, al-Nour, also announced its backing for early elections. The party was once an ally of Morsi but in recent months has broken with him.
Among the opposition crowds outside Qasr el-Qobba, one protester said he believes Morsi will not go easily. "He will only leave after a catastrophe. Lots of blood. And the military is the only party that can force him out then," said Haitham Farouk, an oil company employee joining a protest for the first time.
He said the "epic" crowds showed how Egypt's public has turned against Morsi and his Brotherhood, which opponents claim is the real power behind the president. "This is everybody, not just the educated or the political," Farouk said of the protesters. "They came down because only the brotherhood gained in the past two years.
Morsi may try half-measure to satisfy the army, he said, "but the people are not going back until he leaves. After what we have seen in the past year, we will not settle for less."
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.
Brotherhood spokesperson Gehad el-Haddad said the opposition is to blame for its own woes, failing to perform well in the elections, and has now decided to "brush up to military power".
"We can't keep running elections until [the Brotherhood] loses," he wrote in a Tweet.
He said the opposition should "man up" to its responsibilities and come up with a better strategy "or accept democratic outcomes."
Despite heated rhetoric among many Islamists about standing up to the military, one cleric from the Salafi movement warned against repeating the scenario of Algeria, when the military negated elections that Islamists won in the 1990s, and the Islamists responded with a years-long, bloody insurgency.
The result, Adel Nasr wrote on a Salafi website, was that "more than a hundred thousand were killed and ... their popularity went down", costing Islamists both political power and the power of their religious message.