The US special envoy to Afghanistan and Pakistan is set to step down from his post in December, his spokeswoman said in statement.

Laura Lucas told the AFP news agency on Wednesday Marc Grossman, who has been in the job for two years, would return to private life.

Grossman was appointed by Hillary Clinton, the outgoing secretary of state, after the sudden death of veteran diplomat Richard Holbrooke in December 2010.

"After almost two years in the position, and with Secretary Clinton's agreement, he will return to private life," the statement said.

Clinton thanked Grossman for building "a diplomatic surge" and an intense global focus which "have put in place a network of regional and international support for Afghanistan post 2014 and into the next decade," the statement added.

"His work also helped set the conditions for an Afghan peace process that will enable Afghans to talk with other Afghans in pursuit of a negotiated settlement to end decades of conflict."

Grossman, 61, is credited with the behind-the-scenes efforts that helped persuade Pakistan to reopen its border crossings with Afghanistan to NATO convoys earlier this year after a row over the killing of 24 Pakistani troops in a US air strike.

His work over the past two years had also supported Obama's "objectives to disrupt and defeat al-Qaeda and ensure that Afghanistan can no longer become a safe haven for terrorists", according to the statement.

Ambassador David Pearce, currently principal deputy special representative, will serve as the acting special representative for Afghanistan and Pakistan.

Grossman served at the US embassy in Pakistan from 1977 to 1979.

He also assisted  his predecessor, Holbrooke, in the Dayton peace talks that ended the Bosnian war.

From 2001 to 2005, he served as undersecretary of state for political affairs - the top position for a career diplomat - when he worked to mend US relationships overseas during the Iraq war.

Source: AFP