Pakistan's ISI spy agency is ready to split with the CIA because of its frustration over what it calls heavy-handed pressure and its anger over what it believes is a covert US operation involving hundreds of contract spies, according to an internal document obtained by The Associated Press and interviews with US and Pakistani officials.

Such a move could seriously damage the US war effort in Afghanistan, limit a program targeting al-Qaida insurgents along the Pakistan frontier, and restrict Washington's access to information in the nuclear-armed country.

According to a statement drafted by the ISI, supported by interviews with officials, an already-fragile relationship between the two agencies collapsed following the shooting death of two Pakistanis by Raymond Davis, a US contracted spy who is in jail in Pakistan facing possible multiple murder charges.

"Post-incident conduct of the CIA has virtually put the partnership into question," said a media statement prepared by the ISI but never released. A copy was obtained this week by the AP.

The statement accused the CIA of using pressure tactics to free Davis.

"It is hard to predict if the relationship will ever reach the level at which it was prior to the Davis episode," the statement said. "The onus of not stalling this relationship between the two agencies now squarely lies on the CIA."

The ISI fears there are hundreds of CIA contracted spies operating in Pakistan without the knowledge of either the Pakistan government or the intelligence agency, a senior Pakistani intelligence official told the AP in an interview. He spoke only on condition he not be identified on grounds that exposure would compromise his security.

Pakistan intelligence had no idea who Davis was or what he was doing when he was arrested, the official said, adding that there are concerns about "how many more Raymond Davises are out there."

Davis was arrested January 27 in Lahore after shooting two Pakistanis. A third Pakistani was killed by a US Consulate vehicle coming to assist the American. Pakistan demanded the driver be handed over, but the AP has learned the two US employees in the car now are in the United States.

Davis has pleaded self-defense, but the Lahore police upon completing their investigation said they would seek murder charges. The ISI official told the AP that Davis had contacts in the tribal regions and knew both the men he shot. He said the ISI is investigating the possibility that the encounter on the streets of Lahore stemmed from a meeting or from threats to Davis.

The CIA repeatedly has tried to penetrate the ISI and learn more about Pakistan's nuclear program. The ISI has mounted its own operations to gather intelligence on the CIA's counterterrorism activities

The ISI is now scouring thousands of visas issued to US employees in Pakistan. The ISI official said Davis' visa application contains bogus references and phone numbers. He said thousands of visas were issued to US Embassy employees over the past five months following a government directive to the Pakistan Embassy in Washington to issue visas without the usual vetting by the interior ministry and the ISI. The same directive was issued to the Pakistan embassies in Britain and the United Arab Emirates, he said.

Within two days of receiving that directive, the Pakistani Embassy issued 400 visas and since then thousands more have been issued, said the ISI official. A Western diplomat in Pakistan agreed that a "floodgate" opened for US Embassy employees requesting Pakistani visas.