By Gordon Corera
BBC security correspondent
A 17 October statement posted on an Islamist website claims to be from the Tawhid and Jihad group led by Abu Musab al-Zarqawi.
Is Bin Laden (right) Zarqawi's idol, or his rival?
It begins with a personal pledge of allegiance from Zarqawi and his fighters to Osama Bin Laden. But what is the evidence for his relationship with al-Qaeda - and for his status as the mastermind of the Iraq insurgency?
The statement has not been authenticated and verifying the author of web postings is almost impossible.
But even the suggestion of some kind of alliance marks another twist in the much disputed tale of the relationship between Zarqawi and Bin Laden.
Few have doubted that there have been contacts, but the generally accepted view so far has been that Zarqawi had constructed his own parallel network which may have in some ways been in competition with that of Bin Laden's al-Qaeda.
At one trial in Germany, a witness said that Zarqawi had ordered his followers not to co-operate with al-Qaeda.
Some had even begun to suggest that with Osama Bin Laden now strangely absent from the scene for a prolonged period, Zarqawi could become the new figurehead of the global jihadist movement.
This makes any pledge of loyalty an interesting development. But tracing the history of contacts between Zarqawi and al-Qaeda involves navigating some murky waters.
The Bush administration has been claiming a link between Zarqawi and Bin Laden for a long time but not always with much success.
Zarqawi first came to prominence just before the start of the Iraq war when, in Colin Powell's presentation before the UN Security Council, Zarqawi's presence in Iraq was portrayed as proof of a link between Saddam Hussein's regime and al-Qaeda.
But evidence of strong links both ways - to Saddam on the one side and to al-Qaeda on the other - proved hard to substantiate.
Since the start of the Iraq insurgency, Zarqawi has steadily risen to prominence as the symbol of the Iraq insurgency in the same way Osama Bin Laden has been the symbol of the global Islamist insurgency.
The message posted on 17 October claims that talks have been going on for eight months between al-Qaeda and Zarqawi and encountered many interruptions as Tawhid and Jihad explained its strategy before the final offer of loyalty.
In January of this year, American officials say they found documents from Zarqawi and addressed to al-Qaeda asking for its help in fomenting a sectarian war in Iraq between Shia and Sunni.
The implication was that Zarqawi's group was independent but looking for support. US officials said they believed al-Qaeda had rebuffed these advances.
Even if this new statement was authenticated, what would its significance be? Much of that relates to the question of how far the violence in Iraq is linked to the wider jihadist agenda or whether its roots are more domestic.
Answering this question draws on the question of whether Zarqawi really is the all-powerful mastermind sometimes portrayed.
Many of the most high-profile attacks, whether suicide bombings or kidnappings, have been claimed and attributed to Zarqawi's group.
But some question whether he could really be organising much of the rest of the insurgency.
ZARQAWI IN CONTEXT
20-500: Estimate of size Zarqawi's Tawhid and Jihad group
20,000-40,000: Estimate of size of Iraqi resistance
It is helpful though for the US to personalise the insurgency and emphasise the role of foreign fighters because it makes the link to al-Qaeda, obscuring the sense of a nationalist uprising against American "occupation".
It is not just a question of others perhaps exaggerating his role. Zarqawi himself has proved adept at playing the media.
He has used video messages and taken hostages to maximise the impact of his actions - spreading fear but also elevating his own position as the visible leader of opposition to the US and interim government.
With estimates of the numerical strength of Tawhid and Jihad running from 20 to 500, its unlikely to be the motor behind the lower-profile attacks that make up the bulk of the insurgency.
Estimates of the strength of the entire insurgency points to between 20,000-40,000 people being involved, putting Zarqawi's group in context.
Recent evidence also points to the possibility that the Baathist former regime loyalists may still be playing a more active role than has recently been assumed even if that is in co-operation with Zarqawi.
The reality is also that even if he is responsible for many of the acts he claims, Zarqawi and his group would be unable to operate without support from local communities.
US forces have said their raids on Falluja are aimed at Zarqawi associates
The Iraqi insurgency is made of a continuum of fighters ranging from foreign Islamists with a global agenda to local men fighting for vengeance for their family or community with every shade in between and varying degrees of co-operation between different groups in different locations.
The US and Iraqi interim government will be hoping that recent signs in Falluja that residents have become increasingly angry at the way the presence of foreign fighters has made them a target may be just the beginning of a falling away of support for Zarqawi and others.
However, others caution that an assault on Falluja will only drive the different sides together again.
The possibility of an imminent assault may be the reason for Zarqawi to call on Bin Laden but as such it may also signal desperation as much as strength.