Egyptians streamed to Cairo's Tahrir Square on Tuesday for a mass rally to demand an end to military rule, heightening tension after days of deadly clashes that threaten to derail next week's legislative elections.

In a bid to defuse the crisis, the ruling Supreme Council of the Armed Forces (SCAF) has invited "all the political and national forces" for urgent talks on Tuesday, state media said.

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

Protesters at Tahrir Square, epicentre of the demonstrations that toppled Hosni Mubarak in February, chanted against the SCAF and against the police.

"The interior ministry is a thug!" the protesters shouted, ahead of the rally, scheduled for 4:00 pm (1400 GMT).

Medics said another two people were killed early on Tuesday, bringing the death toll from clashes between security forces and protesters since Saturday to 26.

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 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 government of Prime Minister Essam Sharaf has handed its resignation to the (ruling) Supreme Council of the Armed Forces," cabinet spokesman Mohammed Hegazy said in a statement Monday.

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 earlier 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 mass rally to demand the army cede power was called by the political forces that spearheaded the popular uprising that forced Mubarak out of office in February.

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.

The military is also coming under increasing pressure to halt the violence from abroad, with White House spokesman Jay Carney saying it was important that US ally Egypt move toward democratic elections.

US State Department spokeswoman Victoria Nuland echoed the White House call for "free, fair elections," and expressed the hope the electoral process would remain on schedule.

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

"The secretary general is deeply concerned about the violence in Egypt during the last few days, particularly in Cairo. He deplores the loss of life and the many injuries," said UN spokesman Martin Nesirky.

"The secretary general calls on the transitional authorities to guarantee the protection of human rights and civil liberties for all Egyptians, including the right to peaceful protest."

Tens of thousands of people had packed Cairo's Tahrir Square on Monday night, after clashes continued for a third straight day between protesters and police in and around the square.

They greeted news of the cabinet's resignation with indifference, calling for the removal of the military rulers as clashes continued around the nearby interior ministry headquarters.

Riot police fired volleys of birdshot, rubber bullets and tear gas at demonstrators who used stones and petrol bombs. Other protesters formed a corridor through which the injured were ferried into waiting ambulances.

Two people were killed early on Tuesday in the canal city of Ismailiya, medics said, as state media reported that clashes also erupted in the Mediterranean city of Alexandria.

Hundreds have been injured during the protests that have raged in Cairo, Alexandria, Ismailiya and the canal city of Suez.

The clashes first erupted on Saturday, a day after large crowds staged a peaceful anti-military mass rally at the square, resuming on Sunday and continuing through the night into Monday.

The SCAF, in a statement read out on state television, said it "regretted" what was happening and said it was committed to the elections timetable.