Embattled President Hosni Mubarak defied protesters demanding he step down immediately, announcing he would serve out the last months of his term and "die on Egyptian soil".

He promised not to seek re-election, but that did not calm public fury as clashes erupted between his opponents and supporters.

The protesters, whose numbers multiplied more than tenfold in a single day yesterday for their biggest rally yet, have insisted they will not end their unprecedented week-old wave of unrest until their ruler for nearly three decades goes.

Mr Mubarak's halfway concession - an end to his rule seven months down the road - threatened to inflame frustration and anger among protesters, who have been peaceful in recent days.

In the Mediterranean city of Alexandria, clashes erupted between several hundred protesters and government supporters soon afterwards, according to footage by Al-Jazeera television.

The protesters threw stones at their rivals, who wielded knives and sticks, until soldiers fired in the air and stepped in between them, said local journalist Hossam el-Wakil.

The speech was immediately derided by protesters in Cairo's central Tahrir Square. Watching on a giant TV, protesters booed and waved their shoes over their heads at his image in a sign of contempt. "Go, go, go! We are not leaving until he leaves," they chanted.

In the 10-minute address, 82-year-old Mr Mubarak appeared sombre but spoke firmly and without an air of defeat. He insisted that even if the protests had never happened, he would not have sought a sixth term in September.

Mr Mubarak said he would serve out the rest of his term working "to accomplish the necessary steps for the peaceful transfer of power". He said he would carry out amendments to rules on presidential elections.

The former air force commander vowed not to flee the country, saying: "This is my dear homeland ... I have lived in it, I fought for it and defended its soil, sovereignty and interests. On its soil I will die. History will judge me and all of us."

His announcement came after heavy pressure from his top ally, the US. Soon after the address, President Barack Obama said he had spoken with Mr Mubarak and "he recognises that the status quo is not sustainable and a change must take place".

Mr Obama said he told Mr Mubarak that an orderly transition must be meaningful and peaceful, begin now and include opposition parties.

The US has been struggling to find a way to ease Mr Mubarak out of office while maintaining stability in Egypt, a key ally in the Middle East that has a 30-year-old peace treaty with Israel and has been a bulwark against Islamic militancy.

Mr Mubarak would be the second Arab leader pushed from office by a popular uprising in the history of the modern Middle East, following the ousting last month of the president of Tunisia - another North African nation.

The US ambassador in Cairo, Margaret Scobey, spoke on the phone with Nobel Peace laureate and former United Nations nuclear chief Mohamed ElBaradei, the embassy said.

Mr ElBaradei, a pro-democracy advocate and one of the opposition's most prominent leaders, has taken a key role in formulating the movement's demands. He is also a member of a new committee formed by various factions to conduct any future negotiations on the protesters' behalf once Mr Mubarak steps down.

Yesterday's protest marked a dramatic escalation that organisers said aims to drive Mr Mubarak out by Friday, with more than 250,000 people flooding into Tahrir, - Liberation - Square.

Many travelled from rural provinces, defying a government transport shutdown and roadblocks. They sang nationalist songs, danced, beat drums and chanted the anti-Mubarak slogan "Leave! Leave! Leave!" as military helicopters buzzed overhead. Similar demonstrations erupted in at least five other cities around Egypt.

Soldiers at checkpoints set up at the entrances of the square did nothing to stop the crowds from entering. The military promised on state TV on Monday night that it would not fire on protesters answering a call for a million people to demonstrate, a sign that army support for Mr Mubarak may be unravelling.

The movement to drive Mr Mubarak out was fuelled by deep frustration with an autocratic regime blamed for ignoring the needs of the poor and allowing rampant corruption.

After years of tight state control, protesters emboldened by the Tunisia unrest took to the streets on January 25 and mounted a once-unimaginable series of protests across the nation of 80 million.

Egypt's official death toll from the crisis stood at 97, with thousands injured, though reports from witnesses across the country indicated the actual toll was far higher.

The repercussions were being felt around the Middle East, as other authoritarian governments fearing popular discontent pre-emptively tried to burnish their democratic image.

Jordan's King Abdullah II sacked his government yesterday in the face of smaller street protests, named an ex-prime minister to form a new Cabinet and ordered him to launch political reforms.

And the Palestinian Cabinet in the West Bank said it would hold long-promised municipal elections "as soon as possible".

This morning, hundreds of people were marching in support of President Mubarak.

The small rallies appeared to be the start of an attempt by Mr Mubarak's three million-member National Democratic Party to retake momentum from protesters.

The army separated about 20 Mubarak supporters from about 1,000 pro-democracy protesters in Tahrir Square, Cairo, but Alexandria saw clashes between several hundred protesters and government supporters, Al-Jazeera television footage showed.