Nigerian president Goodluck Jonathan on Sunday dismissed as "blackmail" a call by the suspected leader of the Islamist group Boko Haram for him to resign and convert to Islam, AFP reports. "When Nigerians voted overwhelmingly for President Jonathan in the 2011 general election, they knew they were voting for a Christian," Jonathan's spokesman, Reuben Abati, said. "As president, Jonathan is the leader of both Muslims and Christians. It amounts to sheer blackmail for any individual or group to ask the president ... to convert to Islam." In a video released on Saturday, Boko Haram's Abubakar Shekau told the president, "You should abandon this ungodly power, you should repent and forsake Christianity." Shekau also criticized U.S. president Barack Obama over Washington's decision to label him a "global terrorist." Some U.S. lawmakers have been pushing the Obama administration to label Boko Haram as a whole a terrorist organization, but American diplomats insist the group remains domestically focused. Boko Haram -- which has declared a "war" on Nigerian Christians -- has carried out increasingly frequent and deadly attacks in the country's north that have left hundreds dead. Members of the group are believed to have received training from al Qaeda in the Islamic Maghreb in northern Mali.