By Paul Reynolds
BBC world affairs correspondent
A video statement from one of the London suicide bombers Mohammad Sidique Khan strongly suggests a link between the bombers and al-Qaeda, which has not been established before.
Mohammad Sidique Khan was a teaching assistant in Leeds
Khan's statement and an accompanying one from al-Qaeda number two Ayman al-Zawahri also link the bombs to British foreign policy.
Khan does not specifically mention Iraq but Zawahri does. "We will respond in kind to all those who took part in the aggressions against Iraq, Afghanistan, and Palestine," he states.
An al-Qaeda connection would make the 7 July bombers not just home-grown but foreign-aided as well.
The assumption is therefore that if al-Qaeda made contact with one group of young Muslim extremists in the UK, it could make contact with others. It might already have done so.
Language of a fighter
There are several indications of the al-Qaeda connection.
Firstly, the Arabic TV channel al-Jazeera, which received the tape, attributes it to "the al-Qaeda organisation."
Khan spoke English on the video shown on al-Jazeera news channel
Second, the fact that Khan's statement is accompanied on the tape by one from Zawahri. This strongly supports the view that Khan must have made contact with al-Qaeda elements, probably when he was in Pakistan from November last year to February this year.
It is possible, even probable, that Khan made the tape in Pakistan and came back to the UK determined on his course.
Third, Khan refers on the tape to the al-Qaeda leadership when he talks about "today's heroes beloved Sheikh Osama Bin Laden, Dr Ayman al-Zawahri and Abu Musab al-Zarqawi". Zarqawi is the leader of the al-Qaeda faction in Iraq.
Fourth, the language he uses is that of the dedicated al-Qaeda fighter. He calls himself a soldier and speaks about his religious and political motives. His religious motive is seen in a passage that ends: "I ask you to make du'a [a supplication] to Allah Almighty to accept the work from me and my brothers and enter us into gardens of paradise."
'Scholars of beggary'
His political motive is explained thus: "Your democratically elected governments continuously perpetuate atrocities against my people all over the world."
Zawahri criticised Britain's Muslim leaders
The issue of whether Iraq was his motivation is not entirely cleared up. It certainly appears to be part of it. His statement also speaks about "the bombing, gassing, imprisonment and torture of my people."
His motivation probably includes Iraq but is not confined to it. Khan defines his people as Muslims, so regards attacks on them anywhere as a justification.
Zawahri does make the connection. He states: "The lands and interests of the countries that took part in the aggression against Palestine, Iraq, and Afghanistan are targets for us."
Al-Jazeera also says the tape contains video of fighting, which it says appears to suggest that the makers of the tape want to stress the connection between the bombings in London and what is happening elsewhere.
The al-Qaeda second-in-command also scorns the condemnation of the London bombings by British Muslim leaders whom he describes as "the scholars of beggary".
This shows the detailed analysis he and al-Qaeda make of political developments in the countries they regard as enemies.