Leaders in Washington for nuclear security summit

South Africa's President Jacob Zuma arrives ahead of an upcoming nuclear security summit organised by U.S. President Barack Obama in Washington, at Andrews Air Force Base, Maryland April 11, 2010. The woman on the right is unidentified. [Photo/Agencies] 

U.S. President Barack Obama meets with South African President Jacob Zuma at Blair House in Washington April 11, 2010, ahead of this week's nuclear security summit, as Secretary of State Hillary Clinton (4th R) watches. [Photo/Agencies]  

U.S. President Barack Obama addresses reporters during his meeting with South African President Jacob Zuma at Blair House in Washington D.C. April 11, 2010. [Photo/Agencies]