Leading Egyptian opposition members refused Thursday to negotiate with newly elected Prime Minister Ahmed Shafiq, saying that they would not enter into talks until Egyptian President Hosni Mubarak left office immediately.

Speaking for the first time after a week of  protests across Egypt calling for regime change, Mubarak said Tuesday that he would not seek to extend his 30-year rule and would step down following elections in September.

But Mohamed ElBaradei and the Muslim Brotherhood on Thursday rejected the prime minister's invitation to negotiate, reiterating their condition that Mubarak quit first.

Anti-government demonstrations entered their 10th day on Thursday, with violent clashes spilling into Cairo's Tahrir square, where protesters - unsatisfied by Mubarak's pledge to step down in September - have vowed to stay until the 82-year-old president departs.

There have been media reports that some opposition groups had agreed to  Shafiq's invitation, including the liberal, nationalist Wafd party, which is a legal party. The Brotherhood is banned in Egypt.

"We have refused to meet. Any negotiations are conditional on Hosni Mubarak stepping down and also conditional on security in Tahrir square," ElBaradei said Thursday.

"We would also like to add that we refuse anything that results from this meeting," said Mohammed al-Beltagi, a former member of parliament from the Brotherhood, adding that his group backed the conditions outlined by ElBaradei.

Egyptian soldiers were forced to separate supporters and opponents of Mubarak at the square, deploying infantry to create a buffer zone in an attempt to halt violence between them.

An estimated 150 people have been killed so far and there have been protests across the country. United Nations human rights chief Navi Pillay said up to 300 people may have died.

Egyptian Vice President Omar Suleiman on Wednesday urged the 2,000 demonstrators in Tahrir Square to leave and observe a curfew to restore calm. He said the start of dialogue with the reformists and opposition depended on an end to street protests.