CAIRO - Activists trying to oust Egyptian President Hosni Mubarak played cat-and-mouse with police on the streets into the early hours of Thursday, as unprecedented protests against his 30-year rule entered a third day.

Prominent reform campaigner Mohamed ElBaradei, who lives in Vienna, was expected to return to Egypt on Thursday, an arrival that could galvanise protests that so far have lacked a leader.

At least three protesters and one policeman have died in clashes since they erupted on Tuesday. The protests, inspired by a popular revolt in Tunisia and unprecedented during Mubarak's strong-handed rule, have seen police fire rubber bullets and tear gas at demonstrators throwing rocks and petrol bombs.

In central Cairo on Wednesday demonstrators burned tyres and hurled stones at police. In Suez, protesters torched a government building.

Demonstrations continued well into the night. By the early hours of Thursday, smaller groups of protesters were still assembling in both cities and being chased off by police.

Protesters are promising to hold the biggest demonstrations yet on Friday after weekly prayers.

"Egypt's Muslims and Christians will go out to fight against corruption, unemployment and oppression and absence of freedom," wrote an activist on a Facebook page.

Protesters say they have seen demonstrators dragged away, beaten and shoved into police vans. The Interior Ministry said on Wednesday that 500 had been arrested. An independent coalition of lawyers said at least 1,200 were detained.

REGROUPING

Sometimes police have scrambled to find the means to respond to the protests. In one spot in central Cairo, angry policemen rammed sticks into pavements to break up pieces of concrete for use as projectiles to hurl at protesters.

Protesters have constantly regrouped, using Facebook and Twitter to galvanise and coordinate their demonstrations.

The arrival of ElBaradei, a Nobel Peace Prize-winning former head of the UN nuclear watchdog, gives the opposition a leader of international stature.

"I am going back to Cairo and back onto the streets, because, really, there is no choice. You go out there with this massive number of people and you hope things will not turn ugly, but so far, the regime does not seem to have gotten that message," he said in remarks on US website The Daily Beast.

He said many Egyptians would no longer tolerate Mubarak's government even for a transitional period, and dismissed as "obviously bogus" the suggestion that authoritarian Arab leaders like Mubarak were the only bulwark against Islamic extremism.

"If we are talking about Egypt, there is a whole rainbow variety of people who are secular, liberal, market oriented, and if you give them a chance they will organise to elect a government that is modern and moderate."

Calls for another big protest on Friday gathered 24,000 Facebook supporters within hours of being posted.

Web activists seem to have acted largely independently of more organised opposition movements, including the Muslim Brotherhood, widely seen as having Egypt's biggest grassroots network with its social and charity projects.

"Participation has no religious direction, it is an Egyptian movement," wrote an activist about Friday's planned protest.

Washington, which views Mubarak as a vital ally and bulwark of Middle Eastern peace, has called for calm and, increasingly, urged Egypt to make reforms to meet the protesters demands.

"We believe strongly that the Egyptian government has an important opportunity at this moment in time to implement political, economic and social reforms to respond to the legitimate needs and interests of the Egyptian people," U.S. Secretary of State Hillary Clinton said.

Like Tunisians, Egyptians complain about surging prices, a lack of jobs and authoritarian rulers who have relied on heavy-handed security to keep dissenting voices quiet.

After decades in which Mubarak's rule has never been seriously challenged, Egypt's large, youthful population has grown increasingly restive and bolder in demanding change.

"The people want the regime to fall," protesters chanted.

Egypt's population of some 80 million is growing by 2 percent a year. Two thirds of the population is under 30, and that age group accounts for 90 percent of the jobless. About 40 percent live on less than $2 a day, and a third are illiterate.

A presidential election is due in September. Egyptians assume that the 82-year-old Mubarak plans either to remain in control or hand power to his son Gamal, 47. Father and son both deny that Gamal is being groomed for the job.