In front of tens of thousands of cheering supporters in Cairo's Tahrir Square, Egypt's Islamist President-elect Mohamed Mursi takes a symbolic oath of office on Friday.br br SOUNDBITE: Egypt's Islamist President-elect Mohamed Mursi (Arabic)br br "I swear by God that I will sincerely protect the republican system and that I respect the constitution and the rule of law."br br Mursi will be sworn in officially on Saturday - by the constitutional court - rather than by parliament as usual.br br The court dissolved the Islamist-dominated lower house in a series of measures designed to ensure that the generals who took over from ousted ruler Hosni Mubarak will keep a grip on Egyptian affairs.br br Mursi's speech was a challenge to the army - that also said it represents the will of the people.br br The 60-year-old, U.S.-trained engineer was declared president last Sunday - after he narrowly beat Mubarak's last prime minister.br br Sarah Irwin, Reuters.