Washington (CNN) -- Dennis Ross, one of the president's top advisers dealing with Middle East policy, announced Thursday he's stepping down from his post, leaving prospects for the administration's efforts to restart the peace process even more uncertain.
He cited a promise he made to his wife to serve in the Obama administration for only two years.
Ross, who has held key diplomatic positions during the administrations of George H.W. Bush and Bill Clinton as well as Barack Obama, issued a statement saying, "It has been an honor to work in the Obama administration and to serve this president, particularly during a period of unprecedented change in the broader Middle East."
He added, "Obviously, there is still work to do, but I promised my wife I would return to government for only two years and we both agreed it is time to act on my promise.
"I am grateful to President Obama for having given me the opportunity once again to work on a wide array of Middle Eastern issues and challenges and to support his efforts to promote peace in the region."
Ross's formal title is special assistant to the president and senior director for the "central region," the key area that includes Israel, Afghanistan, Pakistan, the Persian Gulf, and South Asia. His influence is hard to understate, having been handed a portfolio that includes the United States' most pressing national security interests and regions that have undergone significant turmoil over the past two years.
Ross' departure comes at a particularly difficult time for the Obama administration, which has at times clashed with Israeli Prime Minister Benjamin Netanyahu over the Middle East peace process and is dealing with the unpredictable aftermath of the Arab Spring.
The departure also follows that of the special envoy to the Middle East, George Mitchell, who left the administration in May, only days before Netanyahu visited the White House.
During his daily briefing Thursday, White House Press Secretary Jay Carney called Ross a "remarkable contributor to this administration."
"He is ... very much a part and an architect of the sanctions regime and efforts to pressure and isolate Iran, and has been at the forefront of our deliberations about handling the Arab Spring, the remarkable events we have seen in the Middle East and North Africa this year," Carney said.
Asked how Ross' departure would affect the administration's efforts to forge a Middle East peace agreement, Carney said the White House will "build on the good work he has done."