Egyptian state television confirmed Tuesday that Egyptian President Hosni Mubarak is planning to address the nation shortly.
It was not clear what Mubarak would say, but Al-Arabiya television said there were unconfirmed reports that would he "accommodate all the demands made by the people" by not running in the next presidential elections, which are slated for September.
A "senior administration official" in Washington also told CNN that Mubarak would not seek reelection.
Complete Coverage: Anger in the Arab World
Than news came after a day in which at least a quarter-million people - and perhaps as many as 2 million - flooded Cairo's main square Tuesday in a stunning and jubilant array of young and old, urban poor and middle class professionals, mounting by far the largest protest yet in a week of unrelenting demands Mubarak to leave after nearly 30 years in power.
Mubarak has been nearly silent so far in the face of the protests.
The New York Times, citing unnamed U.S. diplomats, reports that U.S. President Barack Obama may have been instrumental in pressuring Mubarak not to seek another term, "effectively withdrawing American support for its closest Arab ally."
The State Department had dispatched a retired senior diplomat - former ambassador to Egypt Frank Wisner - to meet with Egyptian officials, and Wisner delivered Mr. Obama's message to Mubarak himself, the Times reported.
A senior American official told the Associated Press that Wisner told Mubarak the U.S. saw his presidency at an end and urged him to prepare for an orderly transition to real democracy with elections.
Wisner and Mubarak are friends and the official said the retired ambassador made clear that it was the U.S "view that his tenure as president is coming to close."
Tuesday's crowds - determined but peaceful - filled Tahrir, or Liberation, Square and spilled into nearby streets, among them people defying a government transportation shutdown to make their way from rural provinces in the Nile Delta. Protesters jammed in shoulder-to-shoulder, with schoolteachers, farmers, unemployed university graduates, women in conservative headscarves and women in high heels, men in suits and working-class men in scuffed shoes.
They sang nationalist songs and chanted the anti-Mubarak "Leave! Leave! Leave!" as military helicopters buzzed overhead. Organizers said the aim was to intensify marches to get the president out of power by Friday, and similar demonstrations erupted in at least five other cities around Egypt.
The military promised on state TV Monday night that it would not fire on protesters answering a call for a million to demonstrate, and recognized the " ," a sign that army support for Mubarak may be unraveling as momentum builds for an extraordinary eruption of discontent and demands for democracy in the United States' most important Arab ally.
Emboldened by the tacit support of the military, the coalition of groups opposing Mubarak has said that it will consider talks about a transition to democracy only after Mubarak resigns, Al Jazeera reports.
Tens of thousands - and by some reports as many as a million - people gathered in the coastal city of Alexandria in a parallel protest. There were conflicting reports about pockets of violence at that protest, with some observers saying between 100 and 300 people may have been killed.
The United Nations' High Commissioner for Human Rights, Navi Pillay, referred in a statement Tuesday to "unconfirmed reports suggesting as many as 300 people may have been killed so far, more than 3,000 injured and hundreds arrested."
Mubarak, 82, would be the second Arab leader pushed from office by a popular uprising in the history of the modern Middle East, following the ouster last month of Tunisia's president.
The movement to drive Mubarak out has been built on the work of on-line activists and fueled by deep frustration with an autocratic regime blamed for ignoring the needs of the poor and allowing corruption and official abuse to run rampant. After years of tight state control, protesters emboldened by the Tunisia unrest took to the streets on Jan. 25 and mounted a once-unimaginable series of protests across this nation of 80 million people - the region's most populous country and the center of Arabic-language film-making, music and literature.
The repercussions were being felt around the region, as other authoritarian governments fearing popular discontent pre-emptively tried to burnish their democratic image.
Jordan's King Abdullah II in the face of smaller street protests, named an ex-prime minister to form a new Cabinet and ordered him to launch political reforms. The Palestinian Cabinet in West Bank said it would hold long-promised municipal elections "as soon as possible."
The chairman of the powerful U.S. Senate Foreign Relations Committee, Sen. John Kerry, gave public voice to what senior U.S. officials have said only privately in recent days: that Mubarak should "step aside gracefully to make way for a new political structure."
Meanwhile, the Obama administration on Tuesday opened talks with a possible successor to Mubarak, with prominent democracy advocate Nobel Peace laureate Mohamed ElBaradei.
The context of the discussions with Nobel peace laureate Mohamed ElBaradei wasn't immediately public.
The U.S. ambassador in Cairo, Margaret Scobey, spoke by telephone Tuesday, the embassy said. ElBaradei has taken a key role with other opposition groups in formulating the movement's demands for Mubarak to step down and allow a transitional government paving the way for free elections. There was no immediate word on what Scobey and ElBaradei discussed.
"The U.S. Embassy in Cairo has been especially busy in the past several days with an active outreach to political and civil society," State Department spokesman P.J. Crowley said in a message posted to Twitter. "As part of our public outreach to convey support for orderly transition in Egypt, Ambassador Scobey spoke today with Mohamed ElBaradei."
In an interview with Al-Arabiya television, ElBaradei rejected an offer late Monday by Vice President Omar Suleiman for a dialogue on enacting constitutional reforms. He said there could be no negotiations until Mubarak leaves.
ElBaradei, the former head of the U.N. nuclear watchdog, invigorated anti-Mubarak feeling with his return to Egypt last year, but the outlawed Muslim Brotherhood remains Egypt's largest opposition movement.
ElBaradei hailed the armed forces for their "alignment with the people." He said he was speaking on behalf a large portion of the opposition coalition, but did not represent them officially or completely.
"We all know that the first legitimate demand set by the people is the departure of President Mubarak, so that we would start a transitional era, and build a new Egypt on the basis of stability, freedom and democracy," ElBaradei said. "I expect and hope that today's protest would be the last, and that President Mubarak would understand that it is time for him to go in order to avoid more bloodshed."
ElBaradei also signaled a Friday deadline for Mubarak's departure.
Banks, schools and the stock market in Cairo were closed for the third working day, making cash tight. Long lines formed outside bakeries as people tried to replenish their stores of bread, for which prices were spiraling.
An unprecedented shutdown of the Internet was in its fifth day after the last of the service providers abruptly stopped shuttling Internet traffic into and out of the country.
Cairo's international airport remained a scene of chaos as thousands of foreigners sought to flee.
The various protesters have little in common beyond the demand that Mubarak go. Perhaps the most significant tensions among them is between young secular activists and the Muslim Brotherhood, which wants to form a state governed by Islamic law but renounced violence in the 1970s unlike other Islamist groups that waged a violent campaign against the government in the 1980s and 1990s. The more secular are deeply suspicious the Brotherhood aims to co-opt what they contend is a spontaneous, popular movement. American officials have suggested they have similar fears.
"The longer this plays out, the more things begin to unravel … it creates political openings. And what we've learned through history is often not the first phase or even the second phase that matters, it's the third or fourth phase," Dr. Richard Haass, president of the Council on Foreign Relations, told CBS' "The Early Show" Tuesday. "And clearly the religious radicals … [will] try to exploit any political openings, which is why it's important that sooner rather than later a dialogue starts to take place, Mubarak leaves office and order is restored and the economy gets started up again."