More than half of Afghanistan’s 13.5 million eligible cast their votes for president Saturday mostly undisturbed by violence.The pressure on polling stations was heavy enough for voting hours to be extended. Security was provided by 350,000 Afghan troops.In isolated incidents,a roadside bomb killed two policemen and wounded two others in the southern city of Qalat; An explosion at a polling station in the southeastern province of Logar injured four voters, rockets landed not far from a voting center in Ghazni, and in the northern province of Faryub, a would-be suicide bomber was arrested. But Taliban failed to sabotage the election although dozens of people were targeted in advance as a warning to voters. Kabul was sealed off from the rest of the country. The three most prominent contenders to take over from Hamid Karzai at the end of his 12 years as president are former foreign ministers Zalmai Rassoul and Abdullah Abdullah and former finance minister Ashraf Ghani Ahmadzai. The victor will have to lead Afghanistan through the critical final phase of the US military presence in the country. Washington has warned that all US troops will be withdrawn unless Kabul signs a bilateral security accord with the US, which Karzai refused to do. He says he will retire as a private citizen although he is widely expected to wield extensive political influence.