DEVELOPING: The head of Egypt's ruling party says he expects President Mubarak to respond to protester demands.
The New York Times is reporting that President Hosni Mubarak could step aside as soon as tonight and hand over control to his new vice president.
Military officials say the armed forces' supreme council has been meeting all day long and will issue a communique shortly that they say will meet the protesters' demands.
The ruling party chief, Hossan Badrawy, tells The Associated Press he expects Mubarak to address the nation and make a announcement that will satisfy their demands.
Refresh for further updates. Read earlier report below.
Doctors in white lab coats and lawyers in black robes streamed into Cairo's Tahrir Square Thursday, linking striking workers with anti-government protesters to create powerful new momentum for calls to oust President Hosni Mubarak. With its efforts to manage the crisis failing, the government threatened the army could crack down by imposing martial law.
The protests in their 17th day, which have focused on discontent with Mubarak's 29-year monopoly on power, now have tapped into the even deeper well of anger over economic woes, including inflation, unemployment, corruption, low wages and wide economic disparities between rich and poor.
A crowd of 4,000 angry over lack of housing rioted in the Suez Canal city of Port Said on Thursday for a second straight day. They marched on the local state security headquarters, demanded those inside leave, then stormed the building, set fire to part of it and six police cars. Police did not intervene. A day earlier they torched the governor's home and offices.
The spread of labor unrest was in part in direct response to calls from protesters as strikers joined in the movement. But there also seemed to be another element -- locals unleashing long pent-up resentment at specific symbols of the state, whether it was an unpopular local police commander, a state factory seen as stiffing workers or a governor failing to follow through on promises.
The government warnings raised the prospect that the energized protests could bring a new crackdown despite repeated army and government promises not to try to clear protesters from their camp in Cairo's Tahrir Square.
Speaking to the Arab news network Al-Arabiya on Thursday, Foreign Minister Ahmed Aboul Gheit said that if "adventurers" take over the process of reform the military "will be compelled to defend the constitution and national security ... and we'll find ourselves in a very grave situation."
The night earlier, he was more explicit, saying in an interview with "PBS NewsHour" that there would be chaos if Mubarak stepped down immediately. "Do we want the armed forces to assume the responsibility of stabilizing the nation thru imposing martial law, and army in the streets?" he said. It was the second coup warning this week, with Vice President Omar Suleiman making similar threats Tuesday.
The warnings reflect growing government impatience as its own attempts to manage the crisis have failed. Mubarak has refused to step down immediately, saying he will serve out the rest of his term until September elections.
Suleiman has put forward a gradual program for reform in the meantime: Discussions with the opposition over constitutional amendments to be approved by referendum by June, paving the way to the election, in which Mubarak would not run.
But his plan preserves a heavy regime hand in directing the reform process, so protesters have rejected it on suspicion it will not bring real democracy. Youth activists organizing the Tahrir protests have refused any negotiations on reform or halt to demonstrations until Mubarak goes. Not only have they fended off government attempts to fragment their ranks and draw some into talks, their protests have spread.
One of the few groups that did enter talks with Suleiman -- the leftist Tagammu Party -- announced Thursday it had broken off contacts in anger over the coup threats. Tagammu is one of the official, government-sanctioned opposition parties that have little public support and no role in the protests, and are seen by protesters as little more than extensions of the regime.
Youth activists organizing the protests planned to up the pressure on the streets even further, calling for an expanded rally on Friday, hoping to repeat a showing earlier this week that drew about a quarter-million people. Friday's protest was to be expanded, with six separate rallies planned around Cairo, all to eventually march on Tahrir, said Khaled Abdel-Hamid, speaking for a coalition of groups behind the protests.
Thousands were packing the square on Thursday, vowing not to give up until the longtime leader steps down despite a host of sweeping government concessions. At the same time, protest organizers have made a concerted effort to bring labor movements into the protests.
The labor unrest unleashed this week was flaring so quickly that protesters sent out messages to railroad workers not to go on strike and halt trains because people in the provinces wanted to come to Cairo to join the Tahrir rallies.
Strikes have erupted in a wide breadth of sectors -- postal workers, electricity staff and service technicians at the Suez Canal, in factories manufacturing textiles, steel and beverages and hospitals.
A bus strike launched Thursday snarled traffic in Cairo, a city of 18 million where many of its impoverished residents rely on public transport. Few buses were seen on the streets, which were jammed and slow moving because of the extra reliance on cars.
Around 800 public transport workers blocked a main Cairo thoroughfare with a protest, demanding salary increases, and they said at least 3,000 of their co-workers were rallying in other parts of the city.
If demands are not met, "we will join Tahrir and camp there," said one bus driver, Mustafa Mohammed, who said he has been working since 1997 and only earns 550 Egyptian pounds a month, about $93. "We are immersed in debt," he said.
On Thursday, hundreds of doctors in white coats marched down a street from one of the biggest state hospitals, Qasr el-Aini, to Tahrir Sqaure, chanting "Join us, O Egyptian," witnesses said.
From another direction, crowds of lawyers in black robes marched from their union to the square, waving Egyptian flags and circling Tahrir's rounabout with chants of "Mubarak, you pilot, how did you get $70 billion?" -- referring to the president's past as the air force commander.
Egyptians have been infuriated by newspaper reports that the Mubarak family has amassed billions, and perhaps tens of billions of dollars in wealth while, according to the World Bank, about 40 percent of the country's 80 million people live below or near the poverty line of $2 a day. The family's true net worth is not known.
"We demand a trial of Mubarak and his regime; we are protesting corruption," said Mohammed Zarie, one of the lawyers, who said hundreds of lawyers arrived from provinces and planned to spend the night at the square.
Another, Said Bakri, said the pro-government head of the lawyers' union had been keeping them from joining the protests, but that the group of several hundred decided to come anyway. "The head of the union didn't want to," he said. "And now we're united in one goal.
The sun of the people has risen and it will not set again."
In the face of a revolt by journalists over anti-protest propoganda in state media, the pro-government head of the journalists' union, Makram Mohammed Ahmed, said he was going on indefinite leave. The state prosecutor summoned him over lawsuits filed by journalists accusing him of "negligence" in defending journalists' rights.
Employees demonstrated outside the Environment Ministry in a southern Cairo suburb. Some 1500 workers held a strike at the Media City, a center for television and movie production in a satellite city in the desert outside the capital.
The labor strikes come despite a warning by Vice President Suleiman that calls for civil disobedience are "very dangerous for society and we can't put up with this at all."
The protesters filling streets of Cairo and other cities since Jan. 25 have already posed the greatest challenge to the president's authoritarian rule since he came to power 30 years ago. They have wrought promises of sweeping concessions and reforms, a new Cabinet and a purge of the ruling party leadership, but Mubarak refuses their demands that he step down before September elections.
In a gesture to protesters' complaints about corruption, the state prosecutor on Thursday announced a formal investigation of corruption allegations against three former ministers and former senior figure in the ruling party, all purged from their posts since the protests began.
According to state TV, the investigation is targeting former Commerce Minister Rachid Mohammed Rachid, former Tourism Minister Zuhair Garana, and former Housing Minister Ahmed Maghrabi, state TV. Also under investigation is Ahmed Ezz, a steel tycoon and former senior figure in the ruling party who was a close confidant of Mubarak's son Gamal. All are wealthy businessmen who were unpopular among many Egyptians.
The criminal court upheld an order by the state prosecutor to freeze their assets.
U.S.-based Human Rights Watch has said about 300 people have been killed since the protests began, but it is still compiling a final toll.
The White House warned Egypt's leaders to expect unrelenting protests unless they start to show real reforms and a transition to a freer society, dismissing governmental concessions so far as not having met even the minimum threshold of what people want.
Obama administration officials were also increasingly blunt in describing the limits of their leverage, reasserting that the United States is not seeking to dictate events in Egypt -- and that it cannot.
"We're not going to be able to force them do anything," White House spokesman Robert Gibbs told reporters Wednesday.
Still, Gibbs and other officials called on Egypt's leaders to end the harassment of activists, to broaden the makeup of their negotiations with opposition leaders, to lift a repressive emergency law, and to take up a series of other moves the Obama government has requested for days.