CAIRO — Egyptian President Hosni Mubarak declared Thursday he would not step down, saying in a televised speech that he had transferred some executive powers to his vice president but intended to remain in office to oversee reforms to the constitution.

Jubilation turned to fury in downtown Cairo's Tahrir Square, the epicenter of the popular revolt determined to topple Mubarak's regime. Tens of thousands of Egyptians had gathered in hopes of witnessing a historic moment: a 17-day rebellion ending 30 years of authoritarian rule.

Only minutes before Mubarak spoke, the scene in the square had been festive, with throngs of people singing the national anthem and debating whether the military, the vice president or a civilian politician should succeed Mubarak.

But as Mubarak's speech neared its end, the mood turned. Protesters cried, embraced in anguish and pumped their fists in anger. The crowds chanted: "Leave! Leave!"

"This will push the country to the edge of the abyss. Tomorrow, the army will intervene, if it does not, there will be chaos," said one activist, Waleed el-Korumi. "We will lay waste to our country if we march on the palace. It's a case of both sides sticking to its guns and at the end we will lose our nation," he said, though he added that marches would remain peaceful.

One man watching on a big screen took off his shoe and raised it toward Mubarak in disgust. Hundreds immediately did the same.

"He laughed at us," said Mohammed Mamdouh, a 35-year-old teacher who brought his nephew, 14, for what he thought would be a party.

"If he told me that the sun rises, I don't believe him," said Salah Shkeb, a 35-year-old lawyer from Mansour, 100 miles from Cairo, who rented an apartment in the capital to join the uprising.

Like many in Tahrir, Shkeb predicted that protests scheduled for today would be the biggest yet. Minutes after the speech ended, hundreds of young demonstrators began marching out of the square and toward the state television headquarters, which for days has been guarded by a phalanx of tanks.

"They are the liars," the crowd shouted, pointing at the television headquarters building, chanting, "We won't leave, they will leave."

Hundreds more massed outside Mubarak's main administrative palace, Oruba, miles away from Tahrir in the Cairo district of Heliopolis, the first time protesters have marched on it, according to witnesses and TV reports. The residence where Mubarak normally stays when he is in Cairo is inside the palace, though it was not known if he was there.

Mubarak recounted the steps he has taken to satisfy protesters' demands, and cited six articles of the constitution he wanted changed. He said he had ordered the country's attorney general to investigate the deaths of "martyrs" in the violence, which human rights groups have said numbered 300. But he did not say the words protesters, who were watching on an enormous bed sheet screen strung up in Tahrir Square, were expecting to hear.

"I say it again that I have lived for the sake of this nation, protecting the nation and carrying my responsibilities, and Egypt will remain above any individual and above everybody," Mubarak concluded. "Egypt is the land of life and death... I and Egypt will not part until I am buried in its soil."

Speaking after Mubarak, Vice President Omar Suleiman told demonstrators to go home.

U.S. caught off guard

The turn of events clearly caught the Obama administration off guard. Earlier Thursday, CIA Director Leon Panetta had told Congress that he expected Mubarak to resign and President Obama, sounding triumphant, had told an audience in Michigan that "what is absolutely clear is that we are witnessing history unfold. It's a moment of transformation that's taking place because the people of Egypt are calling for change."

But Panetta also had said he had "no specific word" that Mubarak would step down and by day's end it was clear he would not. The White House had no immediate comment.

"We understand that you are under pressure to report something, but this is obviously a dynamic situation so we appreciate your patience. We'll get back to you as soon as we can," a White House spokesman said in an e-mail.

Millions of Egyptians had spent the day expecting an announcement that Mubarak would hand over power to military leadership.

State television had announced earlier that Mubarak would address the nation "within hours" on the 17th day of anti-government protests that have shaken his three-decade grip on power. As news of the impending announcement spread, large crowds of people streamed to Tahrir Square.

Military officials met for several hours Thursday, but Mubarak wasn't in attendance, according to Arab news channels. Prime Minister Ahmed Shafik told state television that Mubarak remained in power and that no decision had been made to remove him.

However, the general secretary of Mubarak's ruling National Democratic Party said that Mubarak would "respond to the people's demands" Thursday night, according to news reports.

In Washington, the National Security Council convened an emergency meeting to discuss Egypt, and until Mubarak's speech there were cheers in Tahrir Square. Wael Ghonim, the Egyptian Google executive whose release from secret detention earlier this week inspired protesters, said on Twitter: "Mission accomplished. Thanks to all the brave young Egyptians."

But that comment was immediately met with skepticism from pro-democracy activists, who said that it was too soon to declare victory. A few minutes later, Ghonim had removed the comment. Hours later, Mubarak spoke.