CAIRO – President Hosni Mubarak defied a quarter-million protesters demanding he step down immediately, announcing Tuesday 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 Tuesday 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.

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 afterward, 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 a local journalist, Hossam el-Wakil.

The speech was immediately derided by protesters in Cairo’s 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. One man screamed, “He doesn’t want to say it, he doesn’t want to say it.”

In the 10-minute address, the 82-year-old Mubarak appeared somber 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.

He 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 will carry out amendments to rules on presidential elections.

Mubarak, a former air force commander, vowed not to flee the country.

“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.”

The step came after heavy pressure from his top ally, the U.S. Soon after Mubarak’s address, President Barack Obama said at the White House that he had spoken with Mubarak and “he recognizes that the status quo is not sustainable and a change must take place.” Obama said he told Mubarak that an orderly transition must be meaningful and peaceful, must begin now and must include opposition parties.

Earlier, a visiting Obama envoy – former ambassador to Egypt Frank Wisner, who is a friend of the Egyptian president – met with Mubarak and made clear to him that it is the U.S. “view that his tenure as president is coming to a close,” according to an administration official, who spoke on condition of anonymity because of the delicacy of the ongoing diplomacy.

Tuesday’s protest marked a escalation that organizers said aims to drive Mubarak out by Friday, with more than 250,000 people flooding into Tahrir.