It was not immediately clear why the widely respected diplomat was leaving.

Crocker, who came out of retirement to become ambassador in Kabul in July 2011, has led diplomatic efforts in Afghanistan at a time when the White House has focused on reducing the U.S. presence there – and on doing so without letting the country slide back into civil war.

Crocker was one of the high-level officials discussing Afghanistan’s future at a NATO summit that concluded on Monday in Obama’s home town of Chicago. There, Western leaders refined their plans to pull most of their troops out of Afghanistan by the end of 2014 and put local forces in charge…

News of Crocker’s departure comes only weeks after Cameron Munter, the U.S. ambassador in Islamabad, informed his staff he would be leaving his post in coming months.