Terror warnings: Who knew what when?

Washington has said it could not have prevented the attacks

In the months leading up to 11 September US agencies and officials received a series of intelligence warnings and reports of suspicious activity

December 2000

Intelligence agencies report "an increase in traffic concerning terrorist activities".

February 2001

Instructors at a flying school in Phoenix, Arizona express concern to Federal Aviation Administration (FAA) officials about the poor English and limited flying skills of one of their students, Hani Hanjour.

Hani Hanjour aroused suspicion at flying school

They believe his pilot's licence may be fraudulent.

The FAA finds it is genuine - but school administrators tell Mr Hanjour he will not qualify for an advanced certificate.

Mr Hanjour allegedly flew a hijacked plane into the Pentagon on 11 September.

April - May 2001

Washington receives a "specific threat" about possible al-Qaeda attacks against US targets in the Middle East, the Arabian peninsular and Europe.

May 2001

The State Department issues a statement on 11 May warning that "American citizens abroad may be the target of a terrorist threat from extremist groups with links to Osama Bin Laden's al-Qaeda organisation."

On 29 May, the department warns US citizens to "take appropriate steps to increase their security awareness to reduce their vulnerability".

June 2001

The FAA issues a warning to airlines of possible hijackings.

The State Department issues a worldwide caution and closes the US embassies in Senegal and Bahrain to the public to "review its security posture".

July 2001

An unnamed FBI agent in Phoenix, Arizona, issues a memo calling for an investigation into the large number of Middle Eastern men enrolled in pilot training programmes.

The agent warns that al-Qaeda could be attempting to place terrorists as pilots, security guards or aircraft maintenance workers.

Condoleezza Rice has defended the government's handling of terror intelligence

However, senior FBI officials pay little attention to the memo.

On 2 July the FBI issues a warning of potential threats overseas and adds that domestic attacks cannot be discounted.

President Bush asks National Security Adviser Condoleezza Rice to review and assess the apparent upsurge in threat warnings.

A counterterrorism group coordinated by the National Security Council meets due to heightened concern over possible attacks in Paris, Turkey and Rome.

The US goes on a heightened state of alert after an apparent threat to President Bush at the G8 summit in Genoa.

August 2001

As the third anniversary of the embassy bombings in Kenya and Tanzania passes, the FBI issues a further warning urging caution.

On 6 August, President Bush receives a report detailing Osama Bin Laden's alleged operating methods, including hijacking. The report is based on intelligence data from a 1998 British report according to officials.

Zacharias Moussaoui: Allegedly trained by al-Qaeda

On 13 August, the FBI arrests Zacharias Moussaoui, a French national who had raised suspicions among instructors at the Pan Am International Flight Academy in Minnesota.

Mr Moussaoui had reportedly paid $6,800 in cash and asked for training on large jets, despite his limited experience.

On 16 August the FAA warns that terrorists may have developed a range of modified mobile phones, key chains and pens for use as weapons.

French intelligence agencies later disclose that they believe Mr Moussaoui to be a radical Islamist, who has trained at al-Qaeda camps in Afghanistan.

He is later charged with being involved in the 11 September attacks.

In late August, the CIA issues an alert to the Immigration and Naturalisation Service over two men it is treating as suspects in the attack on the destroyer USS Cole in Yemen.

However it is later disclosed that one of the men - Khalid al-Midhar - had arrived in the US on 4 July.

The FBI are warned, but fail to track him down.

September 2001

On 7 September, the State Department warns of possible attacks on US military facilities or personnel in Japan and Korea.

An FBI agent who questioned Moussaoui reports a vaguely-defined terrorist plot targeting the World Trade Center to his superiors.