President George W. Bush is deeply saddened by the 4,000 U.S. troops who died in Iraq and assumes responsibility for the decision to begin the war, the White House reported on Monday.

The president said he mourned all the lives that were lost in the Iraq battles and sent his sympathy to all the families affected by these losses.

"It's a sober moment, and one that all of us can focus on in terms of the number of 4,000," White House Dana Perino said, referring to the explosion in Baghdad on Sunday, which killed four more U.S. soldiers, raising the death toll to a new tragic number.

"The president feels each and every one of the deaths very strongly and he grieves for their families," Perino said, according to Reuters. "He obviously is grieved by the moment but he mourns the loss of every single life."

The number of 4,000 deaths came a few days after President Bush had declared in a speech, on the fifth anniversary of the Iraq invasion, that the United States was on the way to victory and that he had no intention of withdrawing any of the troops from Iraq.

White House spokeswoman Dana Perino informed, though, that president Bush might reconsider his decision by Friday. He might continue withdrawing troops after an initial drawdown from 158,000 to 140,000 troops is completed in July.

"The president has said the hardest thing a commander in chief will do is send young men and women into combat, and he's grieved for every lost American life, from the very first several years ago to those lost today," Perino said, according to the Associated Press.

The U.S. death toll reached 1000 in September 2004, 18 months after the invasion started. Then it climbed to 2,000 in October 2005 and to 3,000 in December 2006. It has reached 4,000 on Sunday, after a roadside bomb killed four U.S. soldiers and wounded another in Baghdad. The bomb exploded near the soldiers’ vehicle, while they were patrolling in southern Baghdad around 10 p.m.