Senate Foreign Relations Chairman Sen. John Kerry, D-Mass., President Barack Obama's nominee to become secretary of state, gives a 'thumbs-up' as he arrives on Capitol Hill in Washington, Thursday, Jan. 24, 2013, to testify before his confirmation hearing before the committee to replace Hillary Rodham Clinton. (AP Photo/Pablo Martinez Monsivais)
Secretary of State Hillary Rodham Clinton, right, reacts to seeing Senate Foreign Relations Committee member Sen. John McCain, R-Ariz., left, on Capitol Hill in Washington, Thursday, Jan. 24, 2013, prior to the start of the committee's confirmation hearing for Senate Foreign Relations Chairman Sen. John Kerry, D-Mass. to replace Clinton as secretary of state. (AP Photo/Pablo Martinez Monsivais)
FILE - In this Dec. 20, 2012 file photo, Senate Foreign Relations Chairman John Kerry, D-Mass., leads a hearing on the attack on the U.S. consulate in Benghazi, Libya. The Senate Foreign Relations Committee meets Thursday, Jan. 24, 2013, to consider the nomination of Kerry to be secretary of state. (AP Photo/J. Scott Applewhite)
WASHINGTON (AP) — Sen. John Kerry, President Barack Obama’s nominee for secretary of state, said Thursday that the United States will “do what we must” to prevent Iran from developing a nuclear weapon even as he signaled that diplomacy remains a viable option with Tehran. …