U.S. Secretary of State John Kerry (2nd L), U.S. Under Secretary for Political Affairs Wendy Sherman (2nd R) and staff watch a tablet in Lausanne as U.S. President Barack Obama makes a state address on the status of the Iran nuclear program talks, April 2, 2015. A preliminary nuclear deal between Iran and six world powers is a firm basis for a future accord that could end a 12-year nuclear standoff between Tehran and the West, though details must be worked out, Kerry said on Thursday. REUTERS/Brendan Smialowski/Pool TPX IMAGES OF THE DAY

The Head of the Iranian Atomic Energy Organization Ali Akbar Salehi (2nd R) talks with Hossein Fereydoon, special assistant to the Iranian president, while walking through a garden at the Beau Rivage Palace Hotel during an extended round of talks in Lausanne, April 2, 2015. Major powers and Iran negotiated into the early hours of Thursday on Tehran's nuclear programme two days past their deadline, with diplomats saying prospects for a preliminary agreement were finely balanced between success and collapse. REUTERS/Brendan Smialowski/Pool 

Iranian Foreign Minister Javad Zarif talks to members of the media while walking through a courtyard at the Beau Rivage Palace Hotel during an extended round of talks in Lausanne April 1, 2015. Zarif said on Wednesday that the nuclear talks with the success major powers could succeed if they have political will to resolve Iran's 12-year old nuclear standoff. REUTERS/Brendan Smialowski/Pool 

U.S. Secretary of State John Kerry looks out of his room at the Beau Rivage Palace Hotel during a break during the Iran nuclear program talks in Lausanne April 1, 2015. Six world powers and Iran met again on Wednesday in a bid to reach a preliminary accord on reining in Tehran's nuclear programme, after failing to agree crucial details such as the lifting of U.N. sanctions by a midnight deadline. REUTERS/Ruben Sprich

Iran's Foreign Minister Mohammad Javad Zarif (C on left) and head of the Atomic Energy Organization of Iran Ali Akbar Salehi (C on right) talk outside with aides after a morning negotiation session with U.S. Secretary of State John Kerry over Iran's nuclear programme in Lausanne March 19, 2015. REUTERS/Brian Snyder TPX IMAGES OF THE DAY 

U.S. Secretary of State John Kerry and staff look at a tablet following Iranian nuclear talks at the Swiss Federal Institute of Technology in Lausanne (Ecole Polytechnique Federale De Lausanne) April 2, 2015. Iran and world powers reached a framework on curbing Iran's nuclear programme at marathon talks in Switzerland on Thursday that will allow further negotiations towards a final agreement. REUTERS/Brendan Smialowski/Pool 

Iran's Foreign Minister Javad Zarif gestures as he speaks during a news conference at the Swiss Federal Institute of Technology in Lausanne (Ecole Polytechnique Federale De Lausanne) on April 2, 2015, after Iran nuclear program talks finished with extended sessions. Iran and world powers reached a framework agreement on Thursday on curbing Iran's nuclear programme for at least a decade after eight days of marathon talks in Switzerland. The tentative agreement clears the way for talks on a future comprehensive settlement that should allay Western fears that Iran was seeking to build an atomic bomb and in return lift economic sanctions on the Islamic Republic. REUTERS/Brendan Smialowski/Pool

U.S. Secretary of State John Kerry (L) cycles past the Olympic Museum in Lausanne, March 16, 2015. Kerry and Iranian counterpart Mohammad Javad Zarif held four hours of nuclear talks on Monday in the Swiss city of Lausanne before the Iranian delegation headed to Brussels for meetings with European ministers. REUTERS/Denis Balibouse (SWITZERLAND - Tags: POLITICS SPORT TPX IMAGES OF THE DAY)

A late night view of the Beau Rivage Palace Hotel during an extended round of Iran nuclear talks in Lausanne, April 1, 2015. Major powers and Iran negotiated into the early hours of Thursday on Tehran's nuclear programme two days past their deadline, with diplomats saying prospects for a preliminary agreement were finely balanced between success and collapse. Picture taken April 1, 2015. REUTERS/Brendan Smialowski/Pool TPX IMAGES OF THE DAY

Iranian Foreign Minister Javad Zarif (centre L), U.S. Secretary of State John Kerry (centre R) and European Union High Representative Federica Mogherini (2nd R) arrive to deliver statements after nuclear talks at the Swiss Federal Institute of Technology in Lausanne (Ecole Polytechnique Federale De Lausanne) April 2, 2015. Iran and world powers reached a framework on curbing Iran's nuclear programme at marathon talks in Switzerland on Thursday that will allow further negotiations towards a final agreement. REUTERS/Brendan Smialowski/Pool 

The head of Iranian Atomic Energy Organization Ali Akbar Salehi (R) looks over papers before meetings at the Beau Rivage Palace Hotel March 28, 2015 in Lausanne. Iran and major powers are close to agreement on a 2- or 3-page accord with specific numbers that would form the basis of a long-term settlement aimed at ending a 12-year standoff over Tehran's nuclear ambitions, officials said on Friday. REUTERS/Brendan Smialowski/Pool TPX IMAGES OF THE DAY 

Iranian Foreign Minister Javad Zarif (L) waits to make a statement next to U.S. Secretary of State John Kerry (R), following nuclear talks at the Swiss Federal Institute of Technology in Lausanne (Ecole Polytechnique Federale De Lausanne) April 2, 2015. Iran and world powers reached a framework on curbing Iran's nuclear programme at marathon talks in Switzerland on Thursday that will allow further negotiations towards a final agreement. REUTERS/Brendan Smialowski/Pool 

U.S. Secretary of State John Kerry (2nd R) speaks with U.S. Secretary of Energy Ernest Moniz speak as Iranian Foreign Minister Javad Zarif (not pictured) reads a statement, following nuclear talks at the Swiss Federal Institute of Technology in Lausanne (Ecole Polytechnique Federale De Lausanne) April 2, 2015. Iran and world powers reached a framework on curbing Iran's nuclear programme at marathon talks in Switzerland on Thursday that will allow further negotiations towards a final agreement. REUTERS/Brendan Smialowski/Pool 

Iranian Foreign Minister Javad Zarif smiles as he waits for the start of a meeting with P5+1, European Union and Iranian officials at the Beau Rivage Palace Hotel in Lausanne March 30, 2015, during Iran nuclear talks. REUTERS/Brendan Smialowski/Pool 

U.S. Secretary of State John Kerry waits with others before a meeting with P5+1, European Union and Iranian officials at the Beau Rivage Palace Hotel in Lausanne March 30, 2015, during Iran nuclear talks. REUTERS/Brendan Smialowski/Pool 

US Secretary of State John Kerry (centre L) and US Secretary of Energy Ernest Moniz cross paths during a lunch break in negotiations with Iranian officials on March 27, 2015 in Lausanne. The Iranian and US officials are in Switzerland to continue negotiations on the Iranian nuclear program. REUTERS/Brendan Smialowski/Pool

Russian journalists play a game of giant chess in a courtyard at the Beau Rivage Palace Hotel in Lausanne, April 1, 2015. Iran hopes to conclude talks with six major powers on a preliminary accord on reining in its nuclear programme by Wednesday night, its senior nuclear negotiator said. REUTERS/Brendan Smialowski/Pool TPX IMAGES OF THE DAY

The head of Iranian Atomic Energy Organization Ali Akbar Salehi (R) looks over papers before meetings at the Beau Rivage Palace Hotel March 28, 2015 in Lausanne. Iran and major powers are close to agreement on a 2- or 3-page accord with specific numbers that would form the basis of a long-term settlement aimed at ending a 12-year standoff over Tehran's nuclear ambitions, officials said on Friday. REUTERS/Brendan Smialowski/Pool 

Reporters sit in a hallway as they wait during negotiations on Iran's nuclear programme at the Beau Rivage Palace Hotel in Lausanne, March 31, 2015. The United States said it was prepared to work past a midnight deadline into Wednesday if progress was being made towards clinching a preliminary nuclear deal between Iran and global powers. REUTERS/Brendan Smialowski/Pool 

Hamid Baeedinejad (L), an Iranian official, speaks with the press about negotiations on Iran's nuclear programme outside the Beau Rivage Palace Hotel in Lausanne March 31, 2015. The United States said it was prepared to work past a midnight deadline into Wednesday if progress was being made towards clinching a preliminary nuclear deal between Iran and global powers. REUTERS/Brendan Smialowski/Pool 

U.S. Secretary of State John Kerry arrives at Geneva International Airport March 26, 2015. The United States wants major powers to reach a detailed political understanding with Iran by March 31 to clear the path for a long-term nuclear accord, a senior U.S. official said, while hinting that Washington could be flexible on its format. REUTERS/Brendan Smialowski/Pool TPX IMAGES OF THE DAY