The U.S. suspects that Pakistan retaliated for the humiliating American raid that killed Osama bin Laden by allowing the Chinese military to view the wreckage of a radar-evading helicopter used in the mission.
Pakistan suggested it would do just that within days of the raid May 2 that prompted celebrations in the U.S. but anger and embarrassment in Islamabad.
Three senior U.S. defense officials and a counterterrorism official stressed Monday that while they suspect Pakistan probably followed through on the veiled threat, they have no evidence confirming it.
A Pakistan official denied any technology was shared with China. Speaking on condition of anonymity to discuss intelligence, the official added that Pakistan was aware the U.S. had bin Laden's compound and the helicopter wreckage under round-the-clock surveillance after the raid, so it would know if foreign technical experts had been allowed to examine it.
The stealth rotor technology was not that revolutionary, the Pakistan official said, adding that the only value of the helicopter was the lightweight metal used in its construction.
The helicopter was one of two modified Black Hawks that defense experts said evidently used radar-evading technologies plus noise and heat suppression devices to slip across the Afghan-Pakistan border, avoid detection by Pakistani air defenses and deliver two dozen Navy SEALs into the hiding place of the al-Qaida leader.
One of the choppers crash landed during the mission. Before leaving with bin Laden's corpse, commandos blew up the main body of the chopper, apparently to keep secret its stealth components.
Photos of the wreckage with the tail still visible flashed around the world, drawing immediate chatter among defense experts who noticed it appeared to have previously undisclosed technology.
Pakistan eventually allowed the U.S. to retrieve the wreckage. But before that, Pakistan allowed Chinese military engineers to photograph it and to take samples of the chopper's special "stealth" skin, the international business newspaper Financial Times reported Sunday.
Though U.S. officials said Monday that's not a certainty, two of them said they have assumed for some time that Pakistan showed off the technology, given Chinese overtures to Pakistan at the time and the intense anger and humiliation that Pakistan suffered over the raid.
The pre-dawn raid was viewed by many Pakistanis as a severe national embarrassment delivered by a deeply unpopular America and purposely kept secret from Pakistanis, who had repeatedly denied bin Laden was hiding in their territory. Pakistan has called the operation in its northern city of Abbottabad a violation of its sovereignty, and it threatened to retaliate if there are any similar operations in future.
Two weeks after the raid, Pakistani Prime Minister Yousuf Raza Gilani visited China. Though officials said it was planned well in advance, it highlighted warm relations with Beijing at a time his country's relations with the U.S. had been thrown into crisis.
Pakistan recently acceded to a U.S. demand to give dozens of CIA officers extended visas to operate for the next year in the counterterrorism campaign inside Pakistan. The visas were a confidence-building measure and issued in part to renew counterterrorism efforts damaged by the raid.
The CIA for the first time revealed all the names of the operatives to the Pakistanis as part of the visa agreement, a bid to salvage U.S.-Pakistani intelligence relations damaged by the raid and by the earlier incident with CIA security contractor Ray Davis. He was held after killing two armed Pakistanis he claimed were trying to rob him.