Opposition Umma party leader and presidential candidate Sadeq al-Mahdi walks at the party's headquarters in Khartoum April 2, 2010. Umma Party, one of Sudan's largest opposition parties, said on Friday it would boycott presidential, legislative and gubernatorial polls if government did not meet demands including a four-week postponement within four days. REUTERS/Mohamed Nureldin (SUDAN - Tags: POLITICS ELECTIONS)