WASHINGTON – Veteran diplomat Richard Holbrooke, a special U.S. envoy on the Afghanistan war, remained in critical condition Sunday after surgery to fix a tear in the large artery that moves blood from the heart.

President Barack Obama said in a statement Saturday that he and first lady Michelle Obama were praying for Holbrooke’s recovery. He called Holbrooke “a towering figure in American foreign policy” who has been a critical player in developing the administration’s policy on Afghanistan.

The 69-year-old Holbrooke underwent an additional procedure Sunday to improve circulation. The State Department said he received calls from Afghan President Hamid Karzai and Pakistani President Asif Ali Zardari.

Holbrooke was meeting with Secretary of State Hillary Rodham Clinton about midmorning Friday at the State Department when he collapsed.

“Many people would have succumbed to that. Richard is fighting through. Anyone who knows him, and I was with him Friday morning before this happened, knows how tough and resilient he is and we’re all praying that that quality sees him through now,” Obama adviser David Axelrod told CNN’s “State of the Union” on Sunday.

Doctors at George Washington University Hospital worked more than 20 hours through the day Friday and overnight to repair the tear in Holbrooke’s aorta. The surgery was completed Saturday morning, said State Department spokesman P.J. Crowley.