Tony Blair has named Afghanistan officially for the first time as the country suspected of harbouring those responsible for the US attacks.

His comments came after an extraordinary 15-minute mid-air conversation with President Khatami of Iran - the first time the men had spoken to each other Downing Street later admitted.

While flying to New York, where he met some of the families of British victims from the tragedy, Blair and Khatami discussed the role played by Afghanistan.

The prime minister briefed journalists about the call which had been taken via satellite telephone. The conversation confirmed that relations with Iran, which has long had historic ties with Britain, are beginning to be re-established with the more liberal government which is slowing beginning to emerge.

"I have just put down the phone after a conversation with the president of Iran and that in itself was a remarkable conversation. It was a conversation I could not have imagined having some weeks ago," he told journalists.

"Not simply did he give his full solidarity in terms of what had happened to the USA and his strong condemnation of terrorism, but also said how important it was that out of that we re-build the relationship between our two countries as well,'' said Blair.

Blair said the Khatami was united with Britain against the Taliban because many Iranians had been murdered "by those who are trained in the terrorist camps in Afghanistan" - the first official confirmation that Afghanistan is top of the US target list.

The conversation is likely to have confirmed intelligence reports seen by the prime minister over recent years that it is being used as a training base. Iran has been involved in a series of border skirmishes with the Taliban since it rose to power following the Russian withdrawal.

He revealed that the evidence of the countries and groups involved in the terror attacks would be revealed before any strikes took place.

"There's a very strong sense in which the world of Islam is wanting to join with us in common cause because it recognises that people of all faiths are victims of terrorism. When we present the evidence as to who we believe is responsible for this, as well as evidence of those who harbour or help the people who carried out this attack, you will see very well the justification for the action we take.''

Asked how he felt at the prospect of once more sending British troops into action, the prime minister said: "It is a huge and heavy responsibility but what has heartened me is the understanding I have found from every other leader I have spoken to of the necessity of not flinching from action.''