CAIRO - In his first response to the unrest sweeping his nation, Egypt's president fired his Cabinet Saturday and promised reforms but refused to step down, setting the stage for perhaps even heavier street battles with protesters calling for an end to his nearly 30 years in power.

Four days of the largest anti-government protests in decades exploded into chaos hours earlier. Tens of thousands of Egyptians fed up with crushing poverty, unemployment and corruption poured out of mosques after Friday's noon prayers and battled police with stones and firebombs.

By nightfall, they had burned down and looted the ruling party's headquarters along the banks of the Nile and set fire to many other buildings, roaming the streets of downtown Cairo in defiance of a night curfew enforced by the army.

President Hosni Mubarak, confronted with the most dire threat to his three decades of authoritarian rule, faced his nation in a televised address at midnight, making vague promises of social reform in what is likely to be interpreted as an attempt to cling to power rather than a genuine pledge to solve Egypt's pressing problems.

He also defended his security forces and accused the protesters of plotting to destabilize Egypt and destroy the legitimacy of his regime, outraging those still in the streets well into the night.

"We want Mubarak to go and instead he is digging in further," protester Kamal Mohammad said. "He thinks it is calming down the situation but he is just angering people more."

A heavy police crackdown and other extreme measures by the government - including the shutting down of all Internet and mobile phone services in Cairo and other areas - did not stop the surging crowds. With police beaten back in many places, the government called the army into the streets and imposed a nationwide dusk-to-dawn curfew.

Egypt's crackdown drew harsh criticism from the Obama administration and even a threat Friday to reduce a $1.5 billion foreign aid program if Washington's most important Arab ally escalates the use of force.

Stepping up the pressure, President Barack Obama told a news conference he called Mubarak immediately after his TV address and urged the Egyptian leader to take "concrete steps" to expand rights and refrain from violence against protesters.

"The United States will continue to stand up for the rights of the Egyptian people and work with their government in pursuit of a future that is more just, more free and more hopeful," Obama said.

Throughout Friday, flames rose in cities across Egypt, including Alexandria, Suez, Assiut and Port Said, and security officials said there were protests in 11 of the country's 28 provinces.

Calling the anti-government protests "part of a bigger plot to shake the stability and destroy legitimacy" of Egypt's political system, a somber-looking Mubarak said: "We aspire for more democracy, more effort to combat unemployment and poverty and combat corruption."

His promises fell short of the protesters' demands for him to step down.

"Out, out, out!" protesters chanted in violent, chaotic scenes of battles with riot police and the army - which was sent onto the streets for the first time Friday during the crisis.

Protesters seized the streets of Cairo, battling police with stones and firebombs and burning down the ruling party headquarters. Many defied a 6 p.m. curfew and crowds remained on the streets long after midnight, where buildings and tires were still burning and there was widespread looting.

At least one protester was killed Friday, bringing the toll for the week to eight. Demonstrators were seen dragging bloodied, unconsciousness protesters to waiting cars and on to hospitals, but no official number of wounded was announced.

Nobel Peace laureate Mohamed ElBaradei, a leading pro-democracy advocate, was soaked with a water cannon and briefly trapped inside a mosque after joining the protests. He was later placed under house arrest.

In the capital, hundreds of young men carted away televisions, fans and stereo equipment looted from the National Democratic Party, near the Egyptian Museum, home of King Tutankhamun's treasures. Young men formed a human barricade in front of the museum to protect one of Egypt's most important tourist attractions.

Others around the city looted banks, smashed cars, tore down street signs and pelted armored riot police vehicles with paving stones torn from roadways.

"We are the ones who will bring change," declared 21-year-old Ahmed Sharif. "If we do nothing, things will get worse. Change must come!" he screamed through a surgical mask he wore to ward off the tear gas.

Egypt's national airline halted flights for at least 12 hours and a Cairo Airport official said some international airlines had canceled flights to the capital, at least overnight. There were long lines at many supermarkets and employees limited bread sales to 10 rolls per person.

Options appeared to be dwindling for Mubarak, an 82-year-old former air force commander who until this week maintained what looked like rock-solid control of the most populous Arab nation and the cultural heart of the region.

The scenes of anarchy along the Nile played out on television and computer screens from Algiers to Riyadh, two weeks to the day after protesters in Tunisia drove out their autocratic president. Images of the protests in Tunisia emboldened Egyptians to take to the streets in demonstrations organized over mobile phone, Facebook and Twitter.

The government cut off the Internet and mobile phone services, but that did not keep tens of thousands of protesters from all walks of life from joining in rallies after Friday prayers. The demonstrators were united in rage against a regime seen as corrupt, abusive and uncaring toward the nearly half of Egypt's 80 million people who live below the poverty line.

"All these people want to bring down the government. That's our basic desire," said protester Wagdy Syed, 30. "They have no morals, no respect, and no good economic sense."

Egypt has been one of the United States' closest allies in the region since President Anwar Sadat made peace with Israel at Camp David in 1977.

Mubarak kept that deal after Sadat's assassination and has been a close partner of every U.S. president since Jimmy Carter, helping Washington on issues that range from suppressing Islamist violence to counterbalancing the rise of Iran's anti-American Shiite theocracy.

The Mubarak government boasts about economic achievements: rising GDP and a surging private sector led by a construction boom and vibrant, seemingly recession-proof banks.

But many say the fruits of growth have been funneled almost entirely to a politically connected elite, leaving average Egyptians surrounded by unattainable symbols of wealth as they struggle to find jobs, pay daily bills and find affordable housing.

The uprising united the economically struggling and the prosperous, the secular and the religious. On Friday, several of the policemen even stripped off their uniforms and badges and joined the demonstrators.

The crowd included Christian men with key rings with crosses swinging from their pockets and young men dressed in fast-food restaurant uniforms. Women dressed in black veils and wide, flowing robes followed women with expensive hairdos, tight jeans and American sneakers.

In downtown Cairo, people on balconies tossed cans of Pepsi and bottles of water to protesters on the streets below to douse their eyes, as well as onions and lemons to sniff, to cut the sting of the tear gas.

Junior lawmakers in the ruling party phoned in to national Egyptian TV appealing for calm in the city.

Some of the most serious violence Friday was in Suez, where protesters seized weapons stored in a police station and asked the policemen inside to leave the building before they burned it down. They also set ablaze about 20 police trucks parked nearby. Demonstrators exchanged fire with policemen trying to stop them from storming another police station and one protester was killed in the gun battle.

In Assiut in southern Egypt, several thousand demonstrators clashed with police that set upon them with batons and sticks, chasing them through side streets.

Mubarak has not said yet whether he will stand for another six-year term as president in elections this year. He has never appointed a deputy and is thought to be grooming his son Gamal to succeed him despite popular opposition. According to leaked U.S. memos, hereditary succession also does not meet with the approval of the powerful military.