Islamabad: In a veiled threat, ISI chief Lt Gen Ahmed Shuja Pasha has asked the United States to stop drone attacks in Pakistan’s tribal belt or else it would be forced to retaliate militarily.

The ISI chief, who faced tremendous criticism after killing of al-Qaeda leader Osama bin Laden in the garrison city of Abbottabad, made the statement during a meeting on Saturday between visiting CIA Deputy Director Michael Morell and senior ISI officials.

Pasha took a firm stance with the US on drone strikes, a daily newspaper quoted its sources as saying.

"We will be forced to respond if you do not come up with a strategy that stops the drone strikes," Pasha reportedly told Morell.

Pasha also described a recent incursion by NATO helicopters into Pakistani airspace as a "shock" for defence cooperation between the US and Pakistan.

Morrell also met operational leaders of the ISI and members of the spy agency's recently set-up counter-terrorism division.

Relations between the CIA and ISI were strained even before the May 2 unilateral American raid that killed bin Laden.

CIA contractor Raymond Davis shot and killed two armed Pakistani men in Lahore in January, taking relations between the spy agencies to a new low.

The ISI was embarrassed by the incident involving Davis, who was reported to be tracking groups like the Lashkar-e-Taiba, and has been pressing the US to reveal the extent of its network and activities inside Pakistan.

In order to "induce US cooperation" the ISI threatened to "restrict access" for all US citizens in Pakistan, including asking US contractors to leave the country.

The ISI made it clear that none of those leaving will be allowed to return without the approval of Pakistani intelligence.

The government has decided to introduce a system of storing biometric information of US contractors visiting Pakistan to prevent unauthorised persons from entering the country, the report said.

CIA Deputy Director Morell asked about the wreckage of the US stealth helicopter that was destroyed during the raid against bin Laden. The Pakistani government has agreed to return the wreckage to the US.

Morrell also asked about progress in determining who was involved in supporting and protecting bin Laden in Abbottabad, the report said.

Pakistan and the US might sign a formal agreement on particulars of their cooperation in the war against terrorism.

Previous cooperation has relied on several informal, and sometimes unacknowledged, arrangements, the report said.