Cairo ( CNN ) -- Clashes erupted between demonstrators and security forces in Egypt on Sunday , leaving 51 people dead and more than 260 injured , state media reported . The violence started early Sunday afternoon as Muslim Brotherhood protesters marched in different neighborhoods in Cairo and across the country . In Egypt 's capital , people swam across the Nile River to escape arrest as military armored personnel carriers supported police clearing the streets of protesters . Tear gas filled the air and security forces with batons beat some of the protesters they detained . It was another powerful sign that Egypt 's military-backed interim government will go to almost any measure to shut down the Muslim Brotherhood 's protests . But in nearby Tahrir Square , the scene was drastically different ; throngs of people celebrated Egypt Armed Forces Day at a festive event that included dancing and fireworks . As thousands of Muslim Brotherhood protesters marched along the Nile from Old Cairo toward Tahrir , security forces blocked their path and quickly dispersed the crowd . Health Ministry official Khaled El-Khatib told CNN that the death toll included 19 people killed in Cairo , 20 people killed in Giza , four people killed in Beni Suef and one person killed in Minya . Nationwide , 268 people were injured , state media reported . In a statement , the Muslim Brotherhood 's Freedom and Justice Party decried what it called `` crimes of violence and murder committed today against peaceful protesters , '' adding that it holds the leaders of the coup that ousted former President Mohamed Morsy responsible . Egypt 's Interior Ministry said it had arrested 423 `` rioters '' on Sunday . In September , an Egyptian court banned all activities of the Muslim Brotherhood and froze its finances , drawing complaints from the international community . At the United Nations General Assembly , Egypt 's interim foreign minister sought to quell these concerns . Nabil Fahmy said Egypt will hold elections in the spring . He also argued that the political process is open to all `` as long as they are committed to the renunciation of violence and terrorism and acts of incitement to them . '' On Sunday , protesters from the Muslim Brotherhood said they would accept nothing less than the reinstatement of the government led by Morsy . But supporters of the military in Tahrir Square remained adamant that that should n't happen . Neither side appeared willing to compromise . Violent clashes after relative calm . New Egyptian government to be in place by spring , foreign minister says . CNN 's Catherine E. Shoichet and Emma Lacey-Bordeaux contributed to this report .
NEW : At least 51 people were killed , state media reports . The Muslim Brotherhood 's party says peaceful protesters were slain . Comment: Demonstrators jump into the Nile to escape arrest .