He said that he has seen no hard evidence that suggests otherwise.
On Sunday, Attorney General Eric H Holder claimed that the Pakistani Taliban was "intimately involved" in the botched bombing.
Meanwhile, the US State Department has joined the Pentagon and the White House in assuring Pakistan it remains a key ally in the war against terror.
US Special Representative for Pakistan and Afghanistan Richard Holbrooke said Secretary of State Hillary Clinton never spoke about disrupting economic or military assistance to Pakistan.
He said Clinton's comments have been misunderstood by people.
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