Islamabad:
The CIA station chief in Islamabad, who oversaw the team that spotted Osama bin Laden, has left Pakistan citing medical reasons. However, sources say the reason was the "extremely tense" ties with the head of Pakistan's Inter-Services Intelligence (ISI) Lt Gen Ahmad Shuja Pasha.
This is the second time in seven months that the US agency's senior-most officer has exited the country.
The CIA station chief in Islamabad - one of the agency's most important positions in the world - arrived late last year, after his predecessor left, when a Pakistani official admitted his name had been leaked.
The recently departed station chief oversaw the intelligence gathering that led to the May 2 raid by US special forces in Abbottabad that killed Bin Laden. He had also helped to release Raymond Davis, a CIA contractor who shot dead two men, who Pakistani officials admit were working for the ISI.
The intelligence gathering included a network of "undeclared Pakistani agents" and this created a "lack of trust" with the ISI, reported ABC News. It added that one US official said the CIA chief was "due to depart in a few months, as a result of his poor relations with the Pakistanis."
However, the ABC news report also pointed out that the departure of two CIA station chiefs in such a short span of time "threatens to upset a vital intelligence office."
Both US and Pakistani officials now hope that the CIA station chief's exit will now lead to improved relations between the intelligence agencies of the two countries.
US officials have insisted that the quick turnover will not harm American intelligence efforts in Pakistan. But sources say the ISI continues to punish the CIA for the unilateral raid. In fact Dozens of CIA officials have left Pakistan out of fear of retribution or exposure.
The Pakistani military has also sent back all but a handful of US special operations forces working near the border Afghanistan. And in the past few days, US officials have also been regularly stopped by police in Khyber-Pakhtunkhwa province in Pakistan's North West Frontier Province and sent back to Islamabad, on the grounds that they did not have papers allowing them to travel in the country's northwest.
"Pakistan has been harassing US personnel working in the country for months," complained an American official.
Sources say much of the tension arises from the ISI's belief that the CIA is still running a clandestine network of American and Pakistani intelligence agents without sharing information about their identities or their assignments.
The CIA has pledged to provide that information but Pakistani intelligence officials do not seem to believe their assurances.
"There is no trust," one Pakistani intelligence official said. Pakistani officials recently rounded up at least five Pakistanis accused of helping the CIA launch the raid against Bin Laden. Only one though remains in custody.
There have been some signs of a thaw between the CIA and the ISI. The ISI recently granted 87 visas for CIA officers, bringing the agency back to full strength in Pakistan.
But a US official complained the visas were not good enough as they were single-entry and valid for only a few months.