Washington, May 18 (IANS) New highly-sophisticated stealth drones flew dozens of missions deep inside Pakistan to monitor the mansion of Osama bin Laden, before US commandos stormed the hideout to kill the Al Qaeda leader, a media report said.

Washington Post quoted US officials as saying that the CIA used the unmanned planes that are designed to evade radars and operate at high altitudes.

Clandestine flights were carried out over Osama's high-walled compound in Pakistan's Abbottabad city for months so as to get high-resolution videos that satellites could not provide.

US Navy SEALs undertook a daring raid to kill Osama at his house May 2. The heavily armed commandos had entered Pakistani airspace on board four stealth helicopters, one of which they had to blow up after it developed a snag. The helicopters were designed to fly in undetected.

The stealth drones were used on the moonless night when Osama's compound was attacked. The drones, which are equipped to eavesdrop on electronic transmissions, enabled US officials to monitor the Pakistani response.

The media report said that the new drones went in undetected beyond the boundaries that Pakistan has imposed on other US drones that carry out strikes against militants near the border with Afghanistan.

CIA flew the new stealth aircraft as "they needed to see more about what was going on", which other surveillance platforms didn't allow, a former US official familiar with the operation was quoted as saying.

"It's not like you can just park a Predator (drone) overhead - the Pakistanis would know," the official added.

The media report said the new drones are a significant advance in the capabilities of remotely piloted planes.

Referring to the surveillance on Osama, retired Air Force Lt. Gen. David Deptula said: "It's a difficult challenge trying to secure information about any area or object of interest that is in a location where access is denied."

He said the challenge goes up when the surveillance needs to be continuous, which "makes non-stealthy slow-speed aircraft easier to detect".