Michael Mann, spokesperson for EU foreign policy chief Catherine Ashton spekes to press during closed-door nuclear talks in Vienna, Austria, Tuesday, Feb. 18, 2014. Iran and six world powers are back at the negotiating table eager to come to terms on a comprehensive nuclear deal but deeply divided on what it should look like. The two sides began meeting Tuesday in attempts to build on a first-step accord that temporarily curbs Tehran's nuclear activities in exchange for some sanctions relief. (AP Photo/Ronald Zak)

Michael Mann, spokesperson for EU foreign policy chief Catherine Ashton spekes to press during closed-door nuclear talks in Vienna, Austria, Tuesday, Feb. 18, 2014. Iran and six world powers are back at the negotiating table eager to come to terms on a comprehensive nuclear deal but deeply divided on what it should look like. The two sides began meeting Tuesday in attempts to build on a first-step accord that temporarily curbs Tehran's nuclear activities in exchange for some sanctions relief. (AP Photo/Ronald Zak)