US agencies intercept signs of plans for a new al-Qa'ida attack on anniversary

Just as a year ago, three days before the greatest single terrorist attack in modern history, the "chatter" is getting louder. Once again, US intelligence is picking up an increase in intercepted electronic communications between suspected al-Qa'ida operatives. But it can't answer the key question: if the buzz does indeed herald another attack, where and in what form will it occur?

The difficulty of converting generic warnings of an attack into specific preventive action has been starkly illustrated again this weekend, with the revelation that a Taliban Foreign Ministry official tried in vain last year to warn the US and the United Nations that Osama bin Laden was planning a huge attack on American soil.

The Taliban warning joins a long list of what, with hindsight, seem clear pointers to the suicide hijackings. They range from laconic threats picked up by the National Security Agency 24 hours beforehand that "tomorrow's the day", to the report from the FBI field office in Phoenix, Arizona, as early as February 2001 about a unusual number of Arab men taking flying lessons.

Most glaring of all, perhaps, was the failure of the FBI's Washington headquarters to act upon the specific warning from its Minneapolis office about the suspicious behaviour of the would-be pilot Zacharias Moussaoui, thus far the only person accused of direct involvement.

The fragments, it should be said, were put together to the extent that President Bush was alerted in one daily intelligence briefing at the start of his August 2001 holiday. There were signs that Osama bin Laden was planning to hit US targets in the near future, but the question was which ones and with what weapons. What no one could imagine was four aircraft, loaded with people, turned into missiles. So nothing happened – and the revelation of the ignored warnings from within Afghanistan will only heighten criticism that US intelligence was asleep on the job.

US officials talk of the difference between "strategic" intelligence, which gives the big picture, and "tactical" intelligence which provides the detail. But that explanation is another way of expressing the real problem: America's crippling, in part self-inflicted, shortage of agents and moles inside the terrorist organisations themselves.

The failure stemmed from rules imposed on the CIA making it harder for it to enlist collaborators with a less than squeaky-clean background. They were compounded by the aversion of the FBI and the NSA to hiring foreign language specialists.

Rivalry between the FBI and the CIA did not help – nor did the FBI's antediluvian computer system. President Bush is trying to strengthen America's defences against terrorism by forging a single overarching Department of Homeland Security. But his plans are bogged down in infighting.

It will take more than a bureaucratic shake-up or an equipment upgrade to extract the tiny nuggets of "tactical" gold from the "strategic" earth. In the meantime, however, a Taliban-style warning today would not be dismissed. The risk is now of overreaction.

Desperate to avoid blame, agencies issue "non-specific" terror alerts at the slightest sign of trouble. In doing so, they achieve the worst of both worlds, making the public simultaneously more anxious, yet less inclined to pay attention with every passing alert that proves unfounded.

How the world will remember

America:

New York: Bagpipers will lead a procession to Ground Zero for a service in which the names of each of 2,823 people who died at the site will be read out and an "eternal flame" lit.

Washington: President George Bush and Vice-President Dick Cheney will attend a private ceremony at the Pentagon.

Shanksville, Pennsylvania: President Bush will join 30,000 people where Flight 93 crashed.

Britain:

London: Tony Blair, the Queen and relatives of victims will be at a service at St Paul's Cathedral. The American Church will hold a service at the Methodist Central Hall, Westminster. Firefighters will observe a one-minute silence. Evening ceremony at Regent's Park mosque.

Europe:

Stock exchanges will observe two minutes' silence at 8.46am.

Rome: Service honouring New York firefighters at the Basilica Santa Maria degli Angeli.

Berlin: Chancellor Gerhard Schröder will attend a service at the Berliner Dom Cathedral.

Copenhagen: Two-minute silence, city square.

Stockholm: Swedish Prime Minister Göran Persson will be at a service at the US embassy.

Rest of the world:

Jerusalem: The Israeli museum will open an exhibition of photos from Ground Zero.

Tokyo: A maple tree will be planted outside the US embassy.

Canberra: Special service at St Christopher's Catholic Cathedral.