Health Library: Aortic dissection

Washington (CNN) -- U.S. diplomat Richard Holbrooke has died, a senior administration official told CNN Monday evening.

Holbrooke had undergone surgery in the past three days to repair a tear in his aorta, Secretary of State Hillary Clinton said Monday.

"He had a very serious medical emergency on Friday," Clinton said at a news conference in Quebec, Canada, with foreign ministers from Canada and Mexico. "He has received excellent care including many hours of surgery in the last three days."

Earlier, a State Department official said Holbrooke was "absolutely fighting in an unbelievable way." Holbrooke remains unconscious after an additional procedure to aid circulation following the initial surgery on his aorta, the main artery of the body, the State Department said.

At a holiday reception for U.S. diplomats later Monday, President Barack Obama praised Holbrooke as "simply one of the giants of American foreign policy" who has served the nation "with distinction for nearly 50 years," including his work in negotiating the 1995 Dayton Accords that ended the Bosnian war in the former Yugoslavia.

"As anyone who has ever worked with him knows -- or had the clear disadvantage of negotiating across the table from him -- Richard is relentless," Obama said. "He never stops. He never quits. Because he's always believed that if we stay focused, if we act on our mutual interests, that progress is possible. Wars can end. Peace can be forged."

The president said he and his family were praying for Holbrooke's recovery, "and I know that everyone here joins me when I say that America is more secure -- and the world is a safer place -- because of" his work.

"And 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," Obama said.

Holbrooke, the special U.S. representative on Afghanistan and Pakistan, was getting "fantastic care" at George Washington University Hospital, the State Department official said.

It is the same hospital where Ronald Reagan was taken after being shot in 1981. Holbrooke was taken there Friday after feeling ill at the State Department.

Clinton expressed appreciation for what she called an outpouring of concern and support from "presidents, prime ministers, foreign ministers" who have called the State Department since news of Holbrooke's illness broke.

His surgeon continues to meet with the family to gives frequent updates, and Holbrooke "is receiving great support from a broad and growing community of family and friends," the State Department official said.

"It's remarkable how many messages of support (his wife, Kati Marton) and the family keep receiving from all corners: foreign ministers and ambassadors from around the world, President (Bill) Clinton, senators and congressmen, colleagues from this Af/Pak job, from Vietnam, from the Balkans, from the U.N., from the private sector," the official said.

Clinton and Joint Chiefs Chairman Adm. Mike Mullen have visited the hospital numerous times, according to the State Department source, who said: "They've each come three times, informally chatting with family members, friends and staffers, and really helping to buoy the assembled."

The State Department also said Afghan President Hamid Karzai and Pakistani President Asif Ali Zardari called Holbrooke's wife Sunday morning.

Zardari told CNN's Reza Sayah that Holbrooke is a "fighter." He said he told Holbrooke's wife to be "brave."

"I'm sure he will fight for his life, and he will come out of it," Zardari said.

Asked to reflect on Holbrooke's impact on the Pakistani region, Zardari called him an "extremely hard-working man" who can "get things done which would otherwise take weeks to get through."