Richard Holbrooke, the US envoy to Afghanistan and Pakistan, died Monday after undergoing surgery to repair an aortic tear, CNN reported, citing an administration source.
Holbrooke, 69, collapsed in the office of US Secretary of State Hillary Rodham Clinton on Friday and was rushed to nearby George Washington University Hospital. Holbrooke underwent 20 hours of surgery, State Department spokesman Mark Toner told reporters earlier Monday.
Holbrooke's death comes as US President Barack Obama is preparing to roll out the next steps for the war in Afghanistan, dpa reported.
Shortly before Holbrooke died, his wife Kati and children had attended a holiday reception to honour diplomats with Obama.
Noting his service to the country and the prayers for the recovery of a "tough son of a gun," Obama said that "America is more secure and the world is a safer place - because of the work of Ambassador Richard Holbrooke."
Obama reviewed Holbrooke's nearly 50 years of service to the US, starting as a "young foreign service officer in Vietnam to the architect of the accords that ended the slaughter in the Balkans, to advancing our regional efforts" for peace in Afghanistan and Pakistan.
"He is simply one of the giants of American foreign policy," Obama said.
The diplomat made numerous trips to Afghanistan and Pakistan during the two years he has been the State Department's special envoy. A former ambassador to Germany, Holbrooke also helped broker the 1995 Dayton Peace Accords, which ended the Bosnian civil war.