Leading article: America's excruciating dilemma in Afghanistan

Events of recent days provide a perfect illustration of why it will be so difficult for the US to complete its separate but related missions in Afghanistan – to eradicate the al-Qa'ida leadership in its fastnesses along the border with Pakistan, and to achieve a political settlement that extricates Nato from a long and almost certainly unwinnable war.

This week's report by the CIA into the suicide bombing that killed seven of its operatives at a base in eastern Afghanistan last December paints a depressing picture of security lapses, and the ease with which it was taken in by an al-Qa'ida double agent of whose unreliability it had been warned. But the report also underlines the extreme difficulties faced by the Agency on a terrain no less treacherous than when the 9/11 attacks were conceived and carried out almost a decade ago. Simultaneously, however, a real attempt appears to be underway to reach a political deal, in the shape of talks between the government of President Hamid Karzai and high-level Taliban representatives from both inside Afghanistan and from the group's sanctuaries in Pakistan.

These discussions offer the most realistic exit strategy from the nine-year long war in which US-led Nato forces are making only modest progress at best (despite the near-complete troop surge by the Obama administration). But the path will be long and difficult, with absolutely no guarantee of success. Indeed, as he unveiled the report into the suicide bombing, Leon Panetta, the CIA director, declared that despite the contacts between the two sides, he had seen nothing from the Taliban to suggest a serious effort at reconcilation.

It is easy to share Mr Panetta's scepticism. American misgivings about Mr Karzai himself are well known, while it seems that Mullah Mohammad Omar, the Taliban's most important leader, is being excluded from the talks, because of his close ties with Pakistan's intelligence service. This in turn leads back to the dilemma that pre-dates 9/11 – the complicity between the Taliban and elements of the security services in Islamabad, and the excruciatingly tricky relationship between Washington and its supposed key ally in the so-called "war on terror". US diplomacy has rarely faced a more difficult test.