Islamabad: Admitting a "credibility gap" between Islamabad and Washington, Prime Minister Yousuf Raza Gilani has not ruled out closing Pakistan's airspace to US and said the blockade of the US supply lines into Afghanistan would stay in place for weeks.

The ban on NATO supply lines, already in its third week, would not be lifted until "new rules of engagement" were arrived with US, Gilani said in an interview to BBC.

Asked whether the blockade would continue for days or weeks, the Pakistani Prime Minister replied: "for weeks".

Highlighting that a "credibility gap" existed between Pakistan and the US, Gilani said: "we are working together and still we don't trust each other. I think we have to improve our relations".

Gilani's comments that Pakistan was contemplating shutting its airspace to Americans comes in the wake of Islamabad asking Washington to close down its UAV base at Shamsi in Balochistan, in signs that ties between the two sides continue to be strained after the NATO strike on the Pakistani border post which killed 24 soldiers last month.

Gilani indicated that Pakistan was working to set a new rules of engagement and operation with the US.

"We have a resolve to fight terrorism and therefore we want to set new rules of engagement," he said.

But Gilani stood by declaration that the border incident was a pre-planned attack, a charge rejected by the US.

NATO has apologised for the air strike, calling the attack a "tragic unintended incident".