Washington: The United States on Thursday appreciated the work of outgoing Pakistani Ambassador to the US Hussain Haqqani and said it was looking forward to work with his successor Sherry Rehman.

Haqqani resigned as the Ambassador following allegations that he was instrumental in drafting of a memo on behalf of President Asif Ali Zardari which was delivered to the then Chairman of the Joint Chiefs of Staff Admiral Mike Mullen.

The said memo called for establishing a new security council and expressed apprehension over a military coup after the US operation in Abbottabad that killed Osama bin Laden.

"We are aware of the government of Pakistan's announcement that it intends to appoint Sherry Rehman as the new Pakistani ambassador to the US, and we certainly look forward to working together with her as we continue to build a strong, cooperative relationship between our two countries," State Department spokesperson Mark Toner said.

"I also do want to note that we have appreciated Ambassador Haqqani's strong support for US-Pakistan relations throughout his tenure.

"It's important also to stress that we have not yet received formal notification from the government of Pakistan with respect to Ambassador Haqqani's resignation and the appointment of Rehman. Normal process here is for the Pakistani Embassy or Ministry of Foreign Affairs to send a diplomatic note," he said.

"We very much valued our relationship with Ambassador Haqqani. We look forward to working with Sherry Rehman," Toner told reporters at his daily news conference.

Responding to questions related to the memogate investigations in Pakistan, Toner said this is an internal matter of the country.

"This is a Pakistani issue. I'm not aware of these reports, but it sounds like an internal matter," he said.