"We, as we have said, see this very much as an internal issue relative to Pakistan," Deputy National Security Adviser for Strategic Communications Ben Rhodes told reporters.

"He's been a very close partner, of course, with the United States and we've appreciated the work we've done with him. But at the same time we're certain that we'll be able to work with whom-ever the next Pakistani ambassador is."

Pakistan's government said earlier that it had asked Haqqani to resign and ordered a probe into claims that he sought American help against the country's powerful military.

US Senate Foreign Relations Committee Chairman John Kerry, said in a statement he was "sorry to learn" of Haqqani's resignation.

"He was a strong advocate for his country and the Pakistani people. I respect the Pakistani government's decision, but Ambassador Haqqani's wisdom and insights will be missed here in Washington as we continue to work through the ups and downs of our relationship," said the Democratic lawmaker.