Towards the end of last year US National Security adviser Condoleezza Rice and Defence Secretary Donald Rumsfeld claimed that there were top-level contacts between al-Qaeda and Iraq going back a decade.

Saddam Hussein aids and protects terrorists including members of al-Qaeda George W Bush

State of the Union address

Ms Rice added that prisoners in US custody have said that Iraq had provided "some training to al-Qaeda in chemical weapons development".

No hard evidence was provided for these claims.

In his State of the Union address in late January, President George Bush said: "Evidence from intelligence sources, secret communications, and statements by people now in custody, reveal that Saddam Hussein aids and protects terrorists including members of al-Qaeda."

Again, no concrete evidence was forthcoming.

Establishing this link would go a long way towards persuading sceptical public opinion in the US, Britain and across the world that Iraq represents a clear and imminent security threat to the US and its allies - thereby justifying a war on Iraq.

"Al-Qaeda man seeks medical treatment in Baghdad":
American claims of a link between Iraq and al-Qaeda rest heavily on reports that a Jordanian member of al-Qaeda, Abu Musab al-Zarqawi, sought and received medical treatment in Baghdad after being injured in the fighting in Afghanistan.

There were claims that 11 September attacker Mohamed Atta met Iraqi agents

According to the claims, Mr Zarqawi was refused treatment in Iran. It is reported that communications between Mr Zarqawi and his family in Jordan were intercepted.

There is not any evidence, nor is it claimed, that Mr Zarqawi received anything other than medical treatment in Iraq.

"Al-Qaeda in northern Iraq":
There have been widespread reports that al-Qaeda members have found refuge in northern Iraq. These relate to a group called Ansar al-Islam (Partisans of Islam) which has taken over a small area near the Iranian border.

This part of Iraq, however, is in Kurdish hands and outside the direct control of the Iraqi Government.

Iraq is said by defectors linked to Iraqi opposition groups to have had contacts with the group.

Al-Qaeda interrogations:
US officials have said that al-Qaeda members held by the US authorities at Guantanamo Bay, Diego Garcia and other locations have told their interrogators that Baghdad was attempting to train al-Qaeda in the use of chemical weapons.

There is not independent verification of this. It has also been pointed out that al-Qaeda may be seeking to provoke a US war on Iraq.

"Mohamed Atta in Prague":
For a long time it was claimed that the leader of the 11 September hijackers, Mohamed Atta, had met an Iraqi agent in Prague in April, 2001.

This originated from a report by the Czech authorities.

After an investigation, the Czech President Vaclav Havel concluded that the report could not be substantiated.

First World Trade Centre attack:
There have been claims that Ramzi Yousef, convicted of the World Trade Center bombing in 1993, escaped from New York on a false passport provided by Iraqi intelligence. By its nature, this claim is impossible to prove, or disprove.