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“The US now has information that Pakistan, particularly the ISI, gave access to the Chinese military to the downed helicopter in Abbottabad,” said one person in intelligence circles, referring to the Pakistani spy agency. The Chinese engineers were allowed to survey the wreckage and take photographs of it, as well as take samples of the special “stealth” skin that allowed the American team to enter Pakistan undetected by radar, he said.

President Barack Obama’s national security council had been discussing this incident and trying to decide how to respond, said the situation “doesn’t make us happy”, but the administration had little recourse…

“We had explicitly asked the Pakistanis in the immediate aftermath of the raid not to let anyone have access to the damaged remains of the helicopter,” said the person close to the CIA.

Senior US officials confronted General Ashfaq Kayani, head of the Pakistan military, about this but he flatly denied it, according to a person with knowledge of the meeting.