Pro-democracy activists vowed today to step up the largest anti-government protests in Egypt in three decades, despite mass arrests and mammoth security and as a leading dissident headed to join them.

The protests against the autocratic rule of President Hosni Mubarak, inspired by the groundbreaking "Jasmine Revolution" in Tunisia, have sent shockwaves across the region and prompted Washington to prod its long-time ally on democratic reforms.

Mubarak's ruling National Democratic Party was holding talks on Thursday, according to party members, "to evaluate the situation."

Events on the streets sent jitters Thursday through Egypt's stock exchange, which suspended trading temporarily after a drop of 6.2 percent in the benchmark EGX 30 index, a day after it fell six percent.

Members of the pro-democracy youth group April 6 Movement said they would defy the ban on demonstrations and take to the streets again on Thursday, while calling for mass demonstrations after Friday's Muslim prayers.

Thursday "will not be a holiday... street action will continue," the group said on its Facebook page.

"We've started and we won't stop," one demonstrator told AFP, even as riot police fanned out across central Cairo.

"To continue what we started on January 25, we will take to the streets to demand the right to life, liberty, dignity and we call on everyone to take to the streets ... and to keep going until the demands of the Egyptian people have been met," the group said.

Opposition groups circulated SMS messages and posted appeals on social networking site Facebook for fresh demonstrations "to demand the right to live with freedom and dignity".

By early Thursday afternoon, however, there was no sign of the crowds of protesters that had flooded central Cairo on the previous two days.

According to a security official, at least 1,000 people have been detained around the country since the demonstrations started on Tuesday.

Medics have reported the deaths of six people -- four protesters and two policemen -- in violence linked to the protests, with 55 protesters and 15 police injured.

Egyptian opposition figure and former UN nuclear watchdog chief Mohamed ElBaradei, meanwhile, was due back in Egypt from Vienna and would join in Friday's protests, his brother told AFP.

Ali ElBaradei said his brother, one of Mubarak's most vocal critics, was returning "specifically to participate in protests on Friday."

In a message posted on his Twitter page, Mohamed ElBaradei said he supported continued protests against Mubarak's 30-year-rule.

"We shall continue to exercise our right of peaceful demonstration and restore our freedom and dignity," ElBaradei said. "Regime violence will backfire badly."

Demonstrations in central Cairo continued into the early hours of Thursday, ending when police fired tear gas and made further arrests.

In running battles Wednesday afternoon and into the night, police chased demonstrators through the streets of a popular commercial district in Cairo after the authorities declared a ban on demonstrations.

Protesters responded by throwing rocks at police, damaging several shop fronts in an area near the information ministry.

Protesters in the northeastern port city of Suez threw Molotov cocktails at a government building, setting parts of it on fire, witnesses said.

And dozens were arrested in Egypt's second city of Alexandria as they tried to reach a sea-front square to demonstrate, witnesses said.

The United States, Egypt's chief ally in the Arab world, meanwhile issued a nuanced written statement in Obama's name on Egypt.

"The Egyptian government has an important opportunity to be responsive to the aspirations of the Egyptian people, and pursue political, economic and social reforms that can improve their lives and help Egypt prosper," it said.

"The United States is committed to working with Egypt and the Egyptian people to advance these goals," it added.

The statement also underlined US support for basic democratic freedoms "including the rights to freedom of expression, association and assembly".

Prime Minister Ahmed Nazif said the "government is keen to guarantee freedom of expression through legitimate means", but did not elaborate.

The protests are the largest in Egypt since bread riots in 1977, four years before Mubarak came to power.

Among protesters' demands are the departure of the interior minister, whose security forces have been accused of heavy-handedness; an end to a decades-old state of emergency and a rise in minimum wages.

Political discontent has been rumbling louder than ever in Egypt since parliamentary elections in November, which were widely seen as rigged to allow candidates from Mubarak's ruling National Democratic Party to record a landslide victory.

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