President Barack Obama has called Richard Holbrooke “a towering figure in American foreign policy” and said he is praying for the critically ill diplomat’s recovery.
Mr Holbrooke (69), the president's special envoy for Afghanistan and Pakistan, was described as being in stable, but critical condition after undergoing more than 20 hours of surgery for a torn aorta, the large artery that takes blood from the heart.
The veteran diplomat was meeting with Secretary of State Hillary Rodham Clinton at the State Department on Friday when he suddenly collapsed and was taken to George Washington University Hospital a few blocks away.
Mr Holbrooke was seen walking under his own power to the department's parking garage with a person from State's medical office.