Washington: US has decided to shift its terror-killer drones from Pakistan to Afghanistan after Islamabad asked it to shut down UAV bases on its territory, but America has vowed to continue hitting militants based in Pakistan's tribal areas.

"The withdrawal has not occurred but is expected soon," the official said adding that the drone attacks would then be flown out of Afghanistan where some of them are already based.

Pakistan has asked CIA to take away its personnel from the Shamsi airbase, about 350 kms southwest of Baluchistan's capital Quetta, where some of the drones are based, said senior American officials.

But even after shifting, the Predators and Reapers, top US military commander, Admiral Mike Mullen, in a private meeting in Islamabad last week told Pakistan's powerful army chief Gen Ashfaq Parvez Kayani that CIA would not reduce the drone strikes until Pakistan launched a military operation against the Haqqani network in North Waziristan.

As tensions rises between the two nations, reports said the appointment of General David H Petraeus as America's top spy chief could further inflame relations as Pakistan military does not regard him as a "friend".

The usually secretive Kayani, has made little secret of his distaste for Petraeus, calling him a political general.

Petraeus has privately expressed outrage at what American officials say is the Pakistani main spy agency's most blatant support yet for fighters based in Pakistan who are carrying out attacks against American troops in Afghanistan.

Repairing the frayed ties between the CIA and Pakistan's military-run agency, ISI, will be difficult, American officials say.

"In its current form, the relationship is almost unworkable," said Dennis C Blair, a former American director of national intelligence. "There has to be a major restructuring. The ISI jams the CIA all it wants and pays no penalties."

"The relationship between the two countries is very tense right now," said Representative William M Thornberry of Texas, a senior Republican on the House Armed Services Committee, who visited Pakistan last week.

"And the Pakistan government fuels the anti-American public opinion to increase pressure on us."

Newly disclosed documents obtained by WikiLeaks have also stoked tensions. One of them, from the prison at Guantanamo Bay, Cuba, lists the ISI along with numerous militant groups as allies of Al Qaeda and the Taliban, an indication of how deep American suspicions run when it comes to Pakistani intelligence.

The drone campaign, which the CIA has run against militants in Pakistan's tribal areas since 2004, will now become the preserve of General Petraeus, and it has moved to center stage, at least for the Pakistanis.