WASHINGTON: The United States is holding back some military aid to Pakistan, President Barack Obama's chief of staff confirmed Sunday, after a New York Times report said $800 million was being withheld.

“They've taken some steps that have given us reason to pause on some of the aid which we're giving to the military, and we're trying to work through that,” William Daley told ABC's “This Week with Christiane Amanpour.”

US Secretary of State Hillary Clinton had warned last month that the United States could slow down US military aid to Pakistan unless it took unspecified steps to help the United States.

There has been increasing pressure in Washington on the Obama administration Washington, which provided $2.7 billion in security assistance last year to Islamabad, to hold back on aid.

Growing concerns over collusion with militant groups since it emerged in early May that al Qaeda leader Osama bin Laden was hiding out in a garrison city near Islamabad has been compounded by recent accusations that Pakistan's intelligence services approved a journalist's killing.

According to The New York Times, about $800 million in military aid and equipment, or over one-third of the more than $2 billion in annual US security assistance to Pakistan, could be affected by the suspension.

Asked by ABC about the report, Daley did not dispute the figures and confirmed that some military aid was now being withheld.

“The truth of the matter is, our relationship with Pakistan is very complicated,” he said.

“Obviously there's still a lot of pain that the political system in Pakistan is feeling by virtue of the raid that we did to get Osama bin Laden.

Something that the president felt strongly about. We have no regrets over.

“The Pakistani relationship is difficult, but it must be made to work over time. But until we get through these difficulties, we'll hold back some of the money that the American taxpayers have committed to give.” The New York Times said the suspended aid included about $300 million to reimburse Pakistan for some of the costs of deploying more than 100,000 soldiers along the Afghan border, as well as hundreds of millions of dollars in training assistance and military hardware.