Sick Holbrooke a 'tough son of a gun' : Obama

US President Barack Obama said Monday that critically ill veteran diplomat Richard Holbrooke was a "tough son of a gun" and would put up a tremendous fight for his life in a Washington hospital.

Holbrooke, who has undergone many hours of surgery for a torn aorta, serves as the US special envoy for Afghanistan and Pakistan, after a career spanning nearly 50 years at the pinnacle of US diplomacy.

"We are thinking and praying for you and for Richard every single day," Obama told members of Holbrooke's family at a diplomatic holiday reception at the State Department.

"Richard is relentless, he never stops," Obama said. "America is more secure and the world is a safer place because of the work of Ambassador Richard Holbrooke.

"He is a tough son of a gun so, we are confident that as hard as this is, that he is going to be putting up a tremendous fight."

Earlier, Secretary of State Hillary Clinton said in Canada that Holbrooke, who brokered the Dayton Accords that ended the Bosnian war, remained in stable but "very critical condition."

"He's had excellent care including many hours of surgery in the last three days," Clinton said.

"He is stable but still in very critical condition and we appreciate the outpouring of support and concern that has been evidenced from around the world."

Holbrooke, 69, fell ill on Friday, during a meeting at the State Department.