US believes al-Qa'ida aiming to set Muslim against Muslim

US military authorities said yesterday that the devastating bombings in the holy city of Karbala and in Baghdad seemed to bear the hallmark of al-Qa'ida and the fingerprints of one man.

US military authorities said yesterday that the devastating bombings in the holy city of Karbala and in Baghdad seemed to bear the hallmark of al-Qa'ida and the fingerprints of one man.

The spokesman for the allies in Baghdad, Brigadier General Mark Kimmitt, said a "prime suspect" in the attacks was Abu Musab al-Zarqawi, a Jordanian militant who is believed to be based in Iraq.

Zarqawi has warned of attacks on the majority Shia population with the aim of provoking a Sunni-Shia civil war to wreck the US plans to pull out of Iraq on 30 June. He is already suspected of being behind several major attacks in Iraq.

Last month the Americans gave The New York Times what they said was a letter on a CD-Rom from Zarqawi to his al-Qa'ida superiors - possibly to Osama bin Laden. The memo said that if the Americans did hand over power to Iraqi authorities on that date, the al-Qa'ida fighters in Iraq would lose their raison d'être to wage war.

According to the US military's interpretation of the memo, Zarqawi concluded that if this happened "they will literally have to pack up and go elsewhere" - a tacit admission of defeat for Bin Laden's organisation.

While it is still not known whether the memo is a fake, its predictions look as though they are coming true.

Much of the 11-page memo is devoted to an al Qa'ida-style rant against the Shia. The writer says of the Iraqi Shias: "[They are] the insurmountable obstacle, the lurking snake, the crafty and malicious scorpion, the spying enemy and the penetrating venom. The unhurried observer and the inquiring onlooker will realise that Shi'ism is the looming danger and the true challenge. They are the enemy. Beware of them. Fight them."

But the document also vows to target symbols of the Kurdish community and to accelerate attacks on US troops, policemen and "collaborators' - the Iraqis who work with the Coalition Provisional Authority.

The Shia are identified in the letter as "the key to change. I mean that targeting and hitting them in [their] religious, political and military depth will provoke them to show the Sunnis their rabies ... and bare the teeth of the hidden rancour working in their breasts".

It is then envisaged that the Sunnis would strike back. Zarqawi has a $10m (£5.4m) bounty on his head after being singled out by the Americans as a key link between the ousted regime of Saddam Hussein and al-Qa'ida.

Before the war, the US Secretary of State, Colin Powell, accused Zarqawi of working on chemical weapons in collaboration with Saddam's regime. The British Government never endorsed the US charges of a link between al-Qa'ida and Saddam in the run-up to the war.

After the fall of Saddam, the armed resistance to the US and British occupation was initially blamed on Iraqis still loyal to the ousted dictator. But evidence is mounting of sustained co-operation between foreign Islamic fighters and home-grown militants in Iraq.

This week The Independent obtained a video disc, which is being distributed in Baghdad mosques, which boasts of attacks by non-Iraqis on targets inside Iraq. The video was produced by Jeish Ansar al-Sunna, a little-known group that claimed responsibility for a double suicide bombing in Arbil last month that killed more than 100 people.