Update at 7:08 p.m. ET: Al Arabiya TV reports the Egyptian army may issue a second statement tonight, the BBC says.

Update at 6:06 p.m. ET: Egypt's U.S. ambassador tells CNN that President Hosni Mubarak "has transferred the powers of the presidency to his vice president, who will now undertake all authority as president." That means Vice President Omar Suleiman is the de-facto head of state and the military.

Update at 5:50 p.m. ET: Key opposition figure Mohammad ElBaradei tweets, "Egypt will explode. Army must save the country now."

Foreign Policy has an "exclusive" interview with him.

Update at 5:35 p.m. ET: Protesters have marched from Tahrir Square to the state TV and radio building, Al-Jazeera reports.

Update at 5:11 p.m. ET: Interpreting the earlier Communique #1 of the Supreme Council of the Armed Forces, a senior army field commander said he believes the military is "about to announce, in statement #2, that it has taken over authority in the country, for an interim period, the duration of which is to be determined later," Ahram Online writes.

Asked what a military takeover might mean for Mubarak, Suleiman and Prime Minister Ahmed Shafiq, the commander said, "These are people who have no power over the armed forces."

Update at 4:45 p.m. ET: Al-Masry Al-Youm reports that Egyptian troops and tanks have withdrawn from locations near the presidential palace in Cairo, where they had been stationed since protests began three weeks ago.

Sources said tanks disappeared from Salah Salem Street, near the presidential palace and President Hosni Mubarak's residence.

Angered by Mubarak's defiant speech, protesters are on the march from Tahrir Square in the direction of the state TV building and the palace, several miles from the main square. Other protesters are leaving and could return tomorrow morning for previously planned Friday demonstrations.

Update at 4:40 p.m. ET: Suleiman quote, from the BBC:

"The 25 January movement has succeeded in making a change in the party of democracy, history has begun. Constitutional decisions have been taken, commissions were formed to implement what the president decided in terms of directives in his 1 February speech. "What the president announced today stresses once again his national feeling and his siding with the legitimate demands of the people and his commitment to the many pledges he made in the past. It also proves his awareness of the seriousness of the situation that Egypt is going through. The president had put the supreme interests of the people above everything else."

Update at 4:34 p.m. ET: Vice President Omar Suleiman addresses the nation. He says the protesters have "won" and constitutional changes have been made. "I am committed to doing whatever I can to achieve a peaceful transfer of power."

He calls on Egyptian youths to return to their workplaces and studies.

Update at 4:23 p.m. ET: Angry crowds in Tahrir Square are leaving and may be headed toward the presidential palace or to state TV.

By Doug Stanglin, USA TODAY

Update at 4:20 p.m. ET: In his televised remarks, President Mubarak said he would lift emergency laws "when the time is right." The laws have been used by the government for decades to suppress dissent and intimidate the political opposition.

Update at 4:20 p.m. ET: Al Arabiya TV, citing unidentified sources, reports that Egypt's army will act if protesters refuse a plan of transferring some power from President Hosni Mubarak to Vice President Omar Suleiman.

Update at 4:03 p.m. ET: President Mubarak says in a televised speech this evening that he will not leave office until September elections.

An excerpt:

"I announce in very plain, unequivocal words that I will not run in the coming presidential elections, satisfied with what I have offered to the nation for 60 years, in time of war and peace. I announce that I will adhere to this position and similarly remain adamant to shoulder my responsibility, protecting the constitution, safeguarding the interests of the people until the authority and power is handed over to the person who will be elected in fair and free elections."

Update at 4:03 p.m. ET: Hundreds of thousands of protesters respond to Mubarak's speech with "get out, get out!"

Update at 4:02 p.m. ET: Mubarak says he has delegated "some of the powers" of the presidency to his vice president but does not elaborate.

Update at 4 p.m. ET: Mubarak's speech has touched off full-throated shouts from hundreds of thousands of angry protesters in Tahrir Square.

Update at 3:58 p.m. ET: Mubarak says he speaks "from the heart" in a speech "from father to his children, sons and daughters." He says the changes "we started" can never be reversed.

Update at 3:56 p.m. ET: President Mubarak says he will stay in office to guarantee fair elections in September, while calling for changes in the constitution regarding the electoral process. Crowds jammed into Tahrir Square begin getting restless, start jeering.

Update at 3:51 p.m. ET:President Mubarak says he will remain in office until September presidential elections.

Update at 3:42 p.m. ET: Al Arabiya TV says Mubarak, in his televised remarks, will pledge to ensure conditions for fair and transparent elections.

Update at 3:40 p.m. ET: Al Arabyia TV reports that President Mubarak, in his speech, will announce changes in five constitutional amendments and the elimination of one, among other things.

Update at 3:37 p.m. ET: Al Arabiya TV says Mubarak will transfer power to his vice president, Reuters reports.

Update at 3:35 p.m. ET: Al Arabiya TV says President Mubarak, in his remarks, could announce the lifting of onerous emergency laws and confirms he will not run for president. The TV network says Mubarak "will not accept" foreign interference.

Update at 2:35 p.m. ET: Al-Jazeera TV, which has been broadcasting live pictures of Tahrir Square overflowing with flag-waving protesters, briefly switched this afternoon to Egyptian state TV's broadcast to show viewers what the government station was airing at the moment. For the first time ever, Al-Jazeera reports, state TV was showing the very same shot of crowds swelling the square. This, Al-Jazeera says, reflects a sudden shift from the propagandistic fare state TV has been showing in recent days that tried to largely ignore the protests.

Update at 2:15 p.m. ET: Al Arabiya TV, citing its own correspondent, says President Mubarak will announce constitutional procedures before turning his powers over to his vice president, Omar Suleiman.

Update at 2:05 p.m. ET: Information Minister Anas el-Fiqqi says President Mubarak will not resign, state TV reports, and Prime Minister Ahmed Shafiq says, "Everything is in the hands of President Hosni Mubarak and no decisions have been taken yet." That raises the possibility, the Associated Press writes, that Mubarak could announce a half-measure, such as keeping his title while relinquishing his executive powers.

Update at 1:55 p.m. ET: President Mubarak will address the nation tonight amid rumors that he will step down. One Egyptian newspaper says he will speak at 3 p.m. ET. There are mixed reports on what message he will deliver. NBC reports that Mubarak will leave and turn power over to his new vice president, Omar Suleiman, but Egypt state TV quotes the Egyptian information minister as denying that Mubarak will resign. The main demand for weeks has been Mubarak's ouster.

Update at 1:49 p.m. ET: In brief remarks on events in Egypt, President Obama says, "We are witnessing history unfold."

"The moment of transformation is taking place because the people of Egypt are calling for change," he says.

Obama, who is on a trip to Michigan, says he wants to emphasize to Egyptians that the United States "will continue to do everything that we can to support an orderly and genuine transition to democracy in Egypt."

Update at 1:31 p.m. ET: CNN quotes an Egyptian official as saying the army takeover is "not a coup" but the government will be "outside constitutional authority."

Update at 1:12 p.m. ET: Egyptian state TV quotes Egypt's information minister as denying that President Mubarak will step down, the Associated Press reports.

Update at 12:52 p.m. ET: NBC's Richard Engel reports that for protection, tanks and razor-wire surround the presidential palace in Cairo where President Hosni Mubarak will deliver his speech tonight.

Update at 12:47 p.m. ET: "It looks like a military coup," senior Muslim Brotherhood figure Essam al-Erian tells Reuters. "I feel worry and anxiety. The problem is not with the president. It is with the regime."

Update at 12:37 p.m. ET: USA TODAY's Oren Dorell, in Cairo, reports a crush of people streaming into Tahrir Square, beating drums and chanting, passing between tanks at the entrance, amid reports that President Mubarak will stand down. Protester Ahmed Abdullah, 38, says this means the army will take over and give its leader a dignified exit. "We don't want Egypt to fall into chaos or 60 years backward to a military regime again," he says. "There's some good news and some bad. The good news is freedom, everybody will be heard. The bad news is that it is a military coup which will not be in Egypt's interest at all. The aim of this revolution is to be a free society."

Update at 12:27 p.m. ET: Egyptian state TV reports that President Mubarak is holding talks with Vice President Omar Suleiman, the BBC reports. The BBC reports that Al-Yawn Al-Sabi, a privately owned newspaper in Egypt, quotes "well-informed sources" in Egyptian state TV as saying Mubarak will give a speech at 10 p.m. (3 p.m. ET)

Update at 12:08 p.m. ET: The BBC reports a "party atmosphere" in Cairo's Tahrir Square in anticipation of the resignation of President Hosni Mubarak.

Update at 12:05 p.m. ET: White House spokesman Robert Gibbs, commenting on events in Egypt, says, "We're watching a very fluid situation."

Update at 11:30 a.m ET: Egyptian state TV says President Mubarak will speak to the nation this evening.

Update at 11:30 a.m. ET: USA TODAY's Oren Dorell in Cairo says the military is erecting strands of barbed wire in front of the Ministry of Information TV building, which is surrounded by tanks.

Gamal Mohamed Sayid, 41, an English teacher, said that if, as reported, Mubarak steps down, "All the people will cry with joy."

Update at 11:07 a.m. ET: CNN's John King quotes a senior

U.S. official as saying President Mubarak has agreed to yield power to his vice president, Omar Suleiman.

The BBC quotes a senior member of Egypt's governing party as saying he "hopes" Mubarak will transfer power to Suleiman. Hossan Badrawi, secretary general of the National Democratic Party tells the BBC that Mubarak would "most probably" speak to the nation within hours.

It remains unclear what role the military will have. The Supreme Council of the Armed Forces issued a statement saying it will stay in session indefinitely during the crisis.

An excerpt from the statement:

"Based on the responsibility of the armed forces and its commitment to protect the people and its keenness to protect the nation ... and in support of the legitimate demands of the people [the army] will continue meeting on a continuous basis to examine measures to be taken to protect the nation and its gains and the ambitions of the great Egyptian people.

Update at 11:01 a.m. ET: CIA Director Leon Panetta says there is a "strong likelihood" that President Mubarak will step down today.

Update at 10:50 a.m. ET: Gen. Hassan al-Roueini, military commander for the Cairo area, tells thousands of protesters in central Tahrir Square, "All your demands will be met today."

Many among the flag-waving protesters held up a V-for-victory sign and shouted, "Allahu akbar," or "God is great," the Associated Press reports.

In addition, the head of the ruling party, Hossam Badrawi, tells the AP he expects President Hosni Mubarak will "address the people tonight to respond to protesters' demands."

Update at 10:45 a.m. ET: NBC says Mubarak will make a statement this evening and step down. A statement by the armed forces on Egyptian state TV says the military convened the Supreme Council of the Armed Forces "to safeguard people and protect their interest." Al-Jazeera TV notes that Mubarak was not shown attending that meeting.

In its statement, the military says it the council will remain in session indefinitely during the crisis. It says the decision was made in response to "legitimate" popular demands.

Update at 10:37 a.m. ET: NBC's Richard Engel says two independent sources have confirmed that Mubarak will step down. In addition, the armed forces' Supreme Council has convened to begin the orderly transition of power, NBC says.

Update at 10:28 a.m. ET: NBC reports that Egyptian President Hosni Mubarak will step down tonight and that Vice President Omar Suleiman will take over as president.

Update at 10:23 am ET: Military and ruling party officials say President Hosni Mubarak will meet protesters' demands, the Associated Press reports.

Earlier posts: A senior Egyptian army commander has told protesters that all their demands will be met, the Associated Press reports.

Egypt's Supreme Council of the Armed Forces is meeting to discuss its position on the crisis in Egypt, Al-Jazeera network reports.

Al-Jazeera confirms the AP report and says the army will make a statement today.