Tens of thousands of protesters swarmed Cairo's Tahrir Square on Tuesday to demand an end to military rule, heightening tension amid deadly clashes that threaten to derail parliamentary elections next week.

"Leave!" the huge crowd urged military ruler Field Marshal Hussein Tantawi from the iconic central plaza, where 10 months ago the same call toppled his long-time boss Hosni Mubarak.

One protester hung an effigy of a man in military uniform on a lamp post with a sign that read "the execution of the field marshal."

The Tahrir Square rally came after days of deadly clashes pitting police against protesters demanding democratic change.

Sporadic confrontations continued on the outskirts of the square on Tuesday, with police using batons, tear gas and birdshot to disperse demonstrators.

As the crowd massed, the ruling Supreme Council of the Armed Forces (SCAF) was locked in crisis talks with political groups and discussed the possibility of appointing a new premier after the resignation of Prime Minister Essam Sharaf's cabinet -- which has yet to be accepted.

According to a military source, the two names touted were former UN nuclear watchdog chief Mohamed ElBaradei and Abdelmoneim Abul Futuh, a presidential hopeful and former member of the powerful Muslim Brotherhood.

The Brotherhood, Egypt's best-organised political force, had said it would take part in the talks but there was no indication if those driving the protests attended.

Tantawi, Mubarak's long-serving defence minister who is now the country's de facto ruler, was to address the nation later on Tuesday, state television said.

Those at Tahrir Square indicated they would want to hear nothing less than an announcement of an end to the rule of SCAF, which took over when Mubarak was toppled in a popular revolt in February.

"The people want the downfall of the regime," they shouted, echoing the Arab Spring signature chant.

According to the health ministry, at least 28 people have been killed since Saturday, when the security forces first resorted to tear gas, rubber bullets and birdshot in an bid to subdue the protests, with demonstrators responding by throwing stones and petrol bombs at riot police.

Hundreds have been injured in the protests that spread from Cairo to the Mediterranean city of Alexandria and the canal cities of Ismailiya and Suez.

The United States said it was "deeply concerned" by the violence and called for democratic elections, as watchdog Amnesty International charged the SCAF's record on human rights was worse than that of the Mubarak regime.

Egypt's main stock market index closed down 4.77 percent after trading on the bourse had been suspended for one hour when the main EGX-30 index fell 172.82 points to touch 3,688.17 points, according to the Egyptian Exchange website.

Egypt's military-appointed cabinet of civilian officials announced its resignation late on Monday, but state television quoted a SCAF source as saying this was rejected by the military.

The SCAF said it had asked the justice ministry to set up a committee to probe the violence, and called on "all forces and citizens to commit to (restoring) calm, and creating an atmosphere of stability with the goal of pursuing the political process."

The Brotherhood-affiliated Freedom and Justice Party said it would not participate in Tuesday's protest, a decision it said stemmed from its "desire not to pull people towards fresh bloody confrontations with the parties that are seeking more tension."

Tuesday's rally was called by the activist groups which spearheaded the popular uprising that forced Mubarak out of office.

In a Facebook page for the rally, the groups called for the immediate resignation of Sharaf's cabinet and the formation of a "national salvation" government.

They also demanded a presidential election by April 2012 and a complete overhaul of the interior ministry.

Several politicians, including ElBaradei, have urged the military to review its plans for the transfer of power to civilians, by organising a presidential election before the parliamentary polls which are due to begin next Monday and extend over several months.

But the Muslim Brotherhood, although highly critical of the military rulers, is against any postponement of the legislative vote, feeling it is in a strong position.

The military is also coming under pressure from abroad to halt the violence, with US State Department spokeswoman Victoria Nuland calling for "free, fair elections," and expressing the hope that the polls would remain on schedule.

UN leader Ban Ki-moon urged the military council to "guarantee" civil liberties and he deplored the deaths in the clashes.