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Pakistan receives more than $1 billion in aid annually from the United States, much of it to support its military operations against militants in its tribal regions and along the border with Afghanistan. (Mohammad Zubair/Associated Press)

The United States is suspending some $800 million in military aid to Pakistan amid increased tensions between the two countries since the raid that killed al-Qaeda leader Osama bin Laden.

U.S. President Barack Obama's chief of staff William Daley confirmed the move in a Sunday television interview, saying his country's relationship with Pakistan is "difficult" and must be made "to work over time."

"Until we get through these difficulties, we will hold back some of the money that the American taxpayers have committed to give them," Daley told ABC's This Week.

Pakistan receives some $1.3 billion from the United States in aid every year. But the New York Times reported senior U.S. officials as saying the Obama administration is upset with Pakistan for expelling American military trainers and wants tougher action against the Taliban and others fighting American soldiers in Afghanistan.

Pakistan has been widely criticized by U.S. military and intelligence officials for not being fully committed to weeding out extremists.

The mistrust is so great that U.S. operatives did not inform Pakistani authorities about the May 2 mission deep into Pakistani territory that killed bin Laden, the world's most wanted man for his role in orchestrating the Sept. 11, 2001 attacks.