"Afghans died in a war that's not ours,' Karzai said in the interview published on Sunday, just a month before an election to pick his successor. (Agencies)
He was quoted as saying he was certain the 12-year-old war, America's longest and launched after the attacks of September 11, 2001, was "for the US security and for the Western interest."
Karzai's refusal to sign a security deal with Washington that would permit foreign troops to stay in Afghanistan beyond this year has frustrated the White House, and President Barack Obama has told the Pentagon to prepare for the possibility that no US troops will be left in Afghanistan after 2014.
Obama told Karzai in a phone call on Tuesday he had given the order to the Pentagon. The phone call was the first substantive discussion between the two leaders since June.
But staking out a new position, the White House said in a statement it would leave open the possibility of concluding the bilateral security agreement later this year.
"It's good for them to sign it with my successor," Karzai told the Post. He has insisted the United States must jump-start peace talks with Taliban insurgents and end raids and strikes on Afghan homes before he signs the deal.
The NATO-led force in Afghanistan has a current strength of more than 52,000 soldiers, including 33,600 US troops. More than 3,400 coalition forces have been killed in the fight against the Taliban, including more than 2,300 US troops.
While Afghanistan's police and army are seen as having made big strides in their ability to fight militants, doubts remain about whether they can keep a still-potent Taliban at bay, especially in remote areas.
In the interview, the Afghan leader said he was deeply troubled by the war's casualties, including those in US military operations, and felt betrayed by what he described as an insufficient US focus on going after Taliban sanctuaries in Pakistan rather than in Afghan villages.
Civilian casualties in Afghanistan dissipated his country's "common cause" with the United States, Karzai told the newspaper.
Criticizing his US allies was the only way to secure a response by Washington to his concerns, he added.
The Post said Karzai told his interviewers as he escorted them out of his office on Saturday night: "To the American people, give them my best wishes and my gratitude. To US government, give them my anger, my extreme anger."
"Afghans died in a war that's not ours,' Karzai said in the interview published on Sunday, just a month before an election to pick his successor.