CAIRO (Reuters) – Police fought protesters in two cities in eastern Egypt on Thursday and Nobel Peace Prize winner Mohamed ElBaradei arrived back in the country to join a major demonstration on Friday to try to oust President Hosni Mubarak.

Security forces shot dead a Bedouin protester in the north of Egypt's Sinai region on Thursday, bringing the death toll to five on the third day of protests inspired by unrest which toppled Tunisia's president earlier this month.

In a sign open defiance against authoritarian rulers was spreading, police also clashed with protesters in the Arabian Peninsula state of Yemen and Gabon in West Africa.

Police in Suez fired rubber bullets, water cannon and tear gas at hundreds of demonstrators calling for an end to Mubarak's 30-year-old rule. Protesters chucked rocks and petrol bombs at police lines.

Hundreds of protesters clashed with police in Ismailia, who dispersed the crowds with tear gas, while support spread for a planned wave of protests on Friday initiated on Facebook.

"I will participate," ElBaradei, who has campaigned for reform in Egypt, said on flying in from his home in Vienna, where he used to lead the U.N.'s nuclear watchdog.

"I wish we did not have to go out on the streets to press the regime to act."

A U.S. official said the protests gave Mubarak's government a "great opportunity" to advance political reform. Deputy National Security Adviser Denis McDonough also urged both sides to refrain from violence in the latest sign of U.S. concern.

As in many other countries in the region, protesters in Egypt, a key U.S. ally, complain about surging prices, unemployment and the authorities' reliance on heavy-handed security to keep dissenting voices quiet.

ElBaradei earlier told Reuters in Vienna that it was time for Mubarak to step aside.

"He has served the country for 30 years and it is about time for him to retire," said ElBaradei, who won the peace prize for his work as head of the U.N. nuclear agency.

Arabic satellite channel Al Arabiya said later in a brief screen headline: "ElBaradei: ready to take up power for a transitional period if the street demanded it."

His arrival could spur protesters who have no figurehead, although many activists resent his absences in recent months.

Prime Minister Ahmed Nazif urged citizens to exercise self control on Friday, the cabinet spokesman told reporters.

Egyptians torched a police post in Suez early on Thursday in response to the killing of three demonstrators earlier in the week, a Reuters witness said.

"Our government is a dictatorship. A total dictatorship," said Mohamed Fahim, a 29-year-old glass factory worker, as he stood near the charred skeleton of a car.

"It's our right to choose our government ourselves. We have been living 29 years, my whole life, without being able to choose a president."

On Wednesday evening, people in Suez had tried to burn down a government building, another police post and a local office of Egypt's ruling party before police stopped them. The government has said it intervened there against what it called 'vandalism'.

One policeman has been killed in Cairo in the anti-government protests, unprecedented during Mubarak's rule.

Al-Arabiya said on Thursday Egypt's general prosecutor had charged 40 protesters with trying to "overthrow the regime."

A page on Facebook announcing Friday's protest gained 55,000 supporters in less than 24 hours and the call was then repeated by some opposition groups.

"Egypt's Muslims and Christians will go out to fight against corruption, unemployment and oppression and absence of freedom," wrote an activist on Facebook, which alongside sites like Twitter have been key tools to rally people onto the streets.

Egypt's main stock index suffered the second-biggest one-day fall in its history on Thursday and the prices of two London-listed stocks focused on Egypt also tumbled.

DRAGGED AWAY

Interior Minister Habib al-Adli, whose resignation is being demanded by the protesters, has dismissed the demonstrations.

"Egypt's system is not marginal or frail. We are a big state, with an administration with popular support. The millions will decide the future of this nation, not demonstrations even if numbered in the thousands," he told Kuwait's al-Rai newspaper, according to the newspaper's website.

"Our country is stable and not shaken by such actions."

Witnesses say demonstrators have been 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.

ElBaradei, 68, launched a campaign for change last year, raising hopes his international stature could galvanize the opposition. But many activists have since complained that he should have spent more time on the street than abroad.

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.

'NO RELIGIOUS DIRECTION'

"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 organize to elect a government that is modern and moderate," he said.

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

Washington, which views Mubarak as a vital ally and bulwark of Middle Eastern peace, has called for calm and urged Egypt to make reforms to meet the protesters demands. It fears that Islamic radicals could exploit continuing anger.

Egypt's population is about 80 million, two thirds of them under 30. 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.

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

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.

Egyptian officials denied on Thursday a report that Gamal had fled Egypt.

(Additional reporting by Shaimaa Fayed and Marwa Awad in Cairo, Alexander Dziadosz in Suez and Fredrik Dahl in Vienna; writing by Edmund Blair and Philippa Fletcher, editing by Maria Golovnina)