CAIRO – Egypt's opposition is calling for mass protests Tuesday after Islamists backing President Mohamed Morsi claimed victory in the first round of a referendum it alleges was riddled with polling violations. The opposition coalition, the National Salvation Front, urged Egyptians to “take to the streets Tuesday to defend their freedoms, prevent fraud and reject the draft constitution” ahead of the next round of voting Saturday. It claimed “irregularities and violations” marred the initial stage of the referendum last weekend across half of Egypt that Morsi's Muslim Brotherhood said resulted in a 57 percent “yes” vote, according to its unofficial tally. The official count will be given after the other half of the country goes to the polls in the second round. Mohamed ElBaradei, the Front's coordinator and a Nobel prize laureate, renewed his call for Morsi to cancel the referendum and enter talks with the opposition. “Last chance: Cancel the ill-reputed referendum and begin a dialogue to close the rift, and (appoint) a capable government that can administer, and bring back the state of law,” he wrote on Twitter. A spokesman for ElBaradei's group said the comment was not a call to boycott the second round. Large protests both for and against the proposed constitution have been staged over the past three weeks, sparking several violent clashes and revealing deep divisions in Egyptian society over Morsi's rule. Early this month, eight people died and more than 600 were hurt when rival protesters fought outside the presidential palace in Cairo, prompting the army to deploy troops and tanks to protect it. Some 250,000 soldiers and police have been mobilized to ensure security during the two-stage referendum. The opposition says the constitution weakens human rights, especially those of women, and undermines the independence of judges. – Agencies