The head of the State Department's office in charge of energy diplomacy will step down in August after playing a key role in getting countries such as China, India and Japan to cooperate with Western sanctions on Iran, officials said on Friday.
Carlos Pascual became an important player in Washington's effort to place tough new sanctions on Iran over its disputed nuclear program soon after the bureau of energy resources was launched in 2011.
The State Department said Pascual had decided to return to private life.
He traveled to countries in Asia, Europe and the Middle East with officials from the Departments of Treasury and Commerce to ease the way for sanctions that slashed oil production from one of OPEC's top crude producers.
The sanctions have halved Iran's oil sales since mid-2012 in efforts by the Washington and the European Union to cut funding to the country's nuclear program. The West suspects the program aims to develop a weapon. Iran says the program is for peaceful purposes.
Pascual also led the bureau as the United States became a far larger producer of oil and gas. Soon the United States is expected to be the biggest oil producer, surpassing both Russia and Saudi Arabia, which opens up questions about how Washington will handle the new bounty.
He was formerly ambassador to Mexico and to Ukraine, where he has traveled since Russia invaded and annexed Crimea and worked to find it alternative fuel sources.
His successor could face tough energy diplomacy issues on multiple stages, including in Iraq, where insurgents this week have been taking over cities in the north.
(Reporting by Timothy Gardner; Editing by Lisa Shumaker)