Simon Tisdall is an assistant editor of the Guardian and a foreign affairs columnist.
The extraordinary discovery that Osama bin Laden had been living, possibly since 2005, in a luxury compound in a popular summer resort a short drive from the national capital, Islamabad, is an enormous and dangerous embarrassment for Pakistan's government.
Officials from President Asif Ali Zardari downwards have consistently maintained that the al-Qaida chief was not sheltering on Pakistani soil, suggesting instead that the Americans look for him elsewhere, particularly in Afghanistan. The Pakistani stance was part of a wider policy of denial, dating back to the 9/11 attacks, premised on the argument that Pakistan was not the source and springboard for Islamist-inspired terrorism but rather its principal victim.
Islamabad's head-in-the-sand position, as it is seen by some analysts in the west, has led to intensifying friction with Washington in recent months, as the Obama administration struggles to bring an ordered end to its 10-year involvement in Afghanistan. There have been furious rows about unmanned cross-border drone attacks, the arrest in Lahore of a CIA contractor, and Pakistani criticism of US failure to open peace talks with the Taliban.
But all that is as nothing compared with what may now follow...