US Under Secretary of State for Political Affairs Wendy Sherman leaves after a meeting on February 22, 2015 in Geneva. Washington and Tehran's top diplomats sat down again on February 23 for talks on Iran's nuclear program as they struggled to narrow gaps ahead of a key deadline. AFP PHOTO / FABRICE COFFRINI (Photo credit should read FABRICE COFFRINI/AFP/Getty Images)
WASHINGTON, DC - JULY 29: U.S. Secretary of State John Kerry answers questions about Israel's invasion of Gaza and the current situation in Ukraine following a meeting with Ukrainian Foreign Minister Pavlo Klimkin at the State Department July 29, 2014 in Washington, DC. Kerry responded to questions raised about his attempts to broker a ceasefire between Israel and Hamas. (Photo by Win McNamee/Getty Images)
US President Barack Obama (R) shakes hands with Cuba's President Raul Castro during a meeting on the sidelines of the Summit of the Americas at the ATLAPA Convention center on April 11, 2015 in Panama City. AFP PHOTO/MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images)
WASHINGTON - AUGUST 08: U.S. President Barack Obama pauses as he makes a statement at the State Dining Room of the White House August 8, 2011 in Washington, DC. Obama spoke on the economy, S&P downgrade and the loss of Navy SEAL members in Afghanistan. (Photo by Alex Wong/Getty Images)
WASHINGTON, DC - APRIL 14: Senate Foreign Relations Committee Chairman Sen. Bob Corker (L) (R-TN) confers with ranking member Sen. Ben Cardin (R) (D-MD) during a committee markup meeting on the proposed nuclear agreement with Iran April 14, 2015 in Washington, DC. A bipartisan compromise reached by Corker and Cardin would create a review period that is shorter than originally proposed for a final nuclear deal with Iran and creates compromise language on the removal of sanctions contingent on Iran ceasing support for terrorism. (Photo by Win McNamee/Getty Images)
SEOUL, SOUTH KOREA - FEBRUARY 22: A South Korean student waves a national flag during an anti-Japan rally on February 22, 2014 in Seoul, South Korea. South Korea and Japan are making claim to a set of islands controlled by South Korea, Dokdo or Takeshima, located in the East Sea. The rally was taking place after the Japanese government declared today to be Takeshima Day, further fueling a long-standing territorial row between the two countries. (Photo by Chung Sung-Jun/Getty Images)
US Assistant Secretary of State for Western Hemisphere Affairs Thomas Shannon waits for a press conference at the US embassy in Tegucigalpa, on October 29, 2009. Shannon along with senior adviser on Latin America, Dan Restrepo and representative of the US State Department Craig Kelly visit Honduras in a new push to end the crisis set off by the ouster of President Zelaya exactly four months ago. AFP PHOTO/Yuri CORTEZ (Photo credit should read YURI CORTEZ/AFP/Getty Images)
WASHINGTON, DC - DECEMBER 09: Senate Foreign Relations Committee ranking member Sen. Bob Corker (R-TN) delivers opening remarks during a hearing about a congressional Authorization for the Use of Military Force against the Islamic State, the violent jihadist group that has seized parts of Syria and Iraq, in the Dirksen Senate Office Building on Capitol Hill December 9, 2014 in Washington, DC. Secretary of State John Kerry debated back and forth with senators from both parties about the differences between what Congress is proposing for the AUMF and what the Obama Administration wants. (Photo by Chip Somodevilla/Getty Images)
Senator Rand Paul (R-KY), waves to the crowd of supporters during the kickoff of the National Stand with Rand tour on April 7, 2015 in Louisville, Kentucky. Conservative US Senator Rand Paul announced on April 7 that he is running for his party's nomination for the 2016 presidential race, making him the second major Republican to join the contest. AFP PHOTO / MICHAEL B. THOMAS (Photo credit should read Michael B. Thomas/AFP/Getty Images)
Cuban workers display a portrait of Cuban former President Fidel Castro during May Day celebrations at Revolution Square in Havana on May 1, 2013. About half a million people across Cuba took part in May Day celebrations dedicated to the late Venezuelan president Hugo Chavez, a close ally of the island's communist leaders. President Raul Castro, 81, reviewed a parade in Havana of some 300,000 people bearing banners and flags, from stands erected in the Plaza of the Revolution alongside a giant portrait of Chavez. AFP PHOTO/STR (Photo credit should read STR/AFP/Getty Images)
Medias wait for a statement after Iran nuclear program talks on April 2, 2015 at The Swiss Federal Institutes of Technology (EPFL) in Lausanne. European powers and Iran's foreign minister said Thursday that marathon talks had reached a deal on curtailing Iran's nuclear programme. AFP PHOTO / FABRICE COFFRINI (Photo credit should read FABRICE COFFRINI/AFP/Getty Images)
US Secretary of State John Kerry looks out of the window of his room at the Beau-Rivage Palace hotel during a break in Iran nuclear talks in Lausanne, Switzerland, on April 1, 2015. Iran's chief nuclear negotiator Abbas Araghchi said on April 1 that "problems" remain in nuclear talks with world powers and that there can be no deal without a "framework for the removal of all sanctions". AFP PHOTO / FABRICE COFFRINI (Photo credit should read FABRICE COFFRINI/AFP/Getty Images)
P5+1 ministers, European Union and Iranian officials wait for the opening of a plenary session on Iran nuclear talks at the Beau Rivage Palace Hotel in Lausanne, Switzerland, on March 30, 2015. The top diplomats of Iran and the United States, China, Russia, Britain, France and Germany aim by the end of March 31 to agree the outlines of a deal curtailing Iran's nuclear programme. AFP PHOTO / FABRICE COFFRINI (Photo credit should read FABRICE COFFRINI/AFP/Getty Images)