Pakistan rejects US claims over Saleem Shahzad murder

Information minister Dr Firdous Ashiq Awan said that Adm Mike Mullen's statement was "extremely irresponsible and regrettable."

She said it would cause difficulties in relations between the sides and prove a setback to the war against terror.

US-Pakistan relations have been extremely fraught in recent months.

But Adm Mike Mullen's remarks are the most explicit yet in a downward spiral in recent US-Pakistan relations.

The BBC's Aleem Maqbool in Islamabad says that for a senior American official to say that he believes the authorities were involved heaps further pressure on Islamabad at a time when the Pakistani government's relationship with Washington - on which it has become so reliant for support - is under serious strain.

Mr Shahzad was kidnapped near his home in Islamabad in May. His body was found two days later in Punjab province. At the time, many in the Pakistani media blamed Pakistan's powerful military intelligence agency, the Inter-Services Intelligence (ISI), for the murder. The ISI has denied involvement in the case.

Adm Mullen said he could not confirm if the the ISI was involved.

"I have not seen anything that would disabuse that report that the government knew about this," Adm Mullen told journalists in Washington on Thursday.

"It was sanctioned by the government, yeah," he said