'Strategic advice'

It is looking into ways of engaging Tehran on a broad range of issues from seeking co-operation in Afghanistan to giving up sensitive nuclear work that the West suspects is aimed at building an atomic bomb.

"We must strive to build support for US goals and policies," Wood said.

US government agencies are grappling with how to devise a joint approach to curb Iran's nuclear programme and Ross's role will be to help co-ordinate overall policy.

Wood said Ross would offer "strategic advice" and perspective on the region, co-ordinate new policy approaches and take part in "inter-agency activities".

"Ambassador Ross brings a wealth of experience not just to issues within the region but also to larger political-military challenges that flow from the area and have an impact outside of the Gulf and Southwest Asia, and the secretary looks forward to drawing on that experience and diplomatic perspective," Wood said.

High-profile appointments

Ross is the third high-profile diplomatic adviser or envoy to be appointed to Clinton and Obama.

Last month George Mitchell, a seasoned diplomat and former senator, was appointed special envoy to the Middle East, responsible for Israeli-Palestinian negotiations.

Richard Holbrooke, a veteran diplomat who gained prominence by brokering the peace accords that ended the war in Bosnia, was appointed special representative on Afghanistan and Pakistan.

Ross is currently counsellor at the Washington Institute of Near East Policy and was a US representative on the Israeli-Palestinian peace process during the administrations of Clinton and George Bush.

He also served under Clinton's administration as director of the state department's policy planning staff.