The United States has taken the unprecedented step of sharing with Islamabad surveillance data collected by drones flying over Pakistan, the top US military officer said Thursday.

Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, confirmed at a Senate hearing that Pakistan had requested surveillance support missions by US unmanned aircraft.

"In terms of support and information, they have asked for that, and where they have asked for that, we've supported them," Mullen told the Senate Armed Services Committee.

"Those requests have ceased over the period of about the last month," the admiral said.

He did not explain Islamabad's stance but officials say US military assistance and its drone attacks are a sensitive political subject in Pakistan, with the military and intelligence service divided over Washington's role.

"We're hopeful Pakistan will ask for more help," said a defense official who spoke on condition of anonymity. "But ultimately it's up to them."

Mullen said a New York Times report published Thursday describing the cooperation was an "accurate portrayal."

US drones flying over the Pakistani-Afghan border, including armed Predator aircraft that have bombed Al-Qaeda and related targets, have been a focus of discussions between Washington and Islamabad and a source of tension.

Pakistani officials have pressed to have direct control over the drones and President Asif Ali Zardari acknowledged Wednesday that Islamabad had asked for "ownership" of drones carrying out attacks.

But the United States is not ready to hand over Predators to the Pakistani government, officials said.

"They want the technology but we're willing to share information gathered from the technology," the defense official told AFP.

Mullen said a Los Angeles Times report that suggested Pakistan had been given significant control over targets and operations of armed drones was "completely inaccurate."

In Pakistan, a military spokesman said there had been no deal with Washington on the spy drones.

Analysts say Pakistan quietly works with Washington, sharing intelligence while publicly maintaining a more skeptical line.

"There is better cooperation I think under the surface than what is often acknowledged publicly," said Seth Jones, an analyst at Rand Corporation, the California-based think tank.

Predators run by the Central Intelligence Agency are regularly flown covertly in Pakistan, targeting Al-Qaeda militants. Officials say the US military does not participate in the armed drones program inside Pakistan.

Pakistani officials say the drone strikes, which have killed more than 390 people in about 42 attacks since August 2008, violate its territorial sovereignty and deepen resentment in the nuclear-armed nation.

US intelligence officers, however, are opposed to joint operations with Pakistan, saying information shared several years ago about planned Predator attacks had been leaked to militants.

Instead, the US military proposed to increase the amount of surveillance information shared with Pakistan in a bid to build trust between the two countries' security services.

The initiative culminated with a demonstration surveillance mission by a Predator drone operated by the US military in Afghanistan, during which information from the flight was transmitted to a border coordination center operated by Americans, Pakistanis and Afghans, defense officials said.

President Barack Obama's administration has resisted sharing information about how to operate the drones, even with allies.

Armed US drones have become a crucial weapon against Al-Qaeda targets in Pakistan, but analysts warn the bombing campaign risks fomenting anger against the Pakistani government and the United States.

At the Senate hearing, Mullen said Washington also had increased its efforts to assist the Pakistan military fight Taliban militants, focusing on improving maintenance for helicopters, providing night vision goggles and training.

Defense Secretary Robert Gates told the same hearing that while some big weapons systems were being scaled back, his proposed defense budget calls for a major increase in funding for unmanned aircraft.

The drones have played a vital role in the wars in Iraq and Afghanistan, Gates said.