The news that Pakistan allowed China access to remnants of the top secret US stealth helicopter downed in the raid to kill Osama bin Laden is a sign of the deep mistrust between Islamabad and Washington. While the incident may not mark a definitive breach, it does signal a further downward spiral in relations that both sides need to contain.

As provocative as Pakistan’s move may seem, its military significance is uncertain. How useful the exercise was for China depends not just on the state of the remnants, but also on whether anything it learned matched gaps in its knowledge of stealth technology. This is not rudimentary: Robert Gates, the then defence secretary, found his visit to China in January overshadowed by the first test flight of China’s own J-20 stealth fighter.

US-Pakistani relations have been fraying for some time. The most dramatic deterioration occurred after the bin Laden raid, which was a humiliation both for Pakistan’s military and for its civilian leaders. But even before this, ties were strained: the jailing in February of a CIA contractor who killed two armed Pakistanis in Lahore sparked a tit-for-tat between the countries’ security services.