Nothing could have greater importance in winning the "war on terror" than progress in the Middle East peace process, Tony Blair has said.
Mr Blair has long called for lasting peace in the Middle East
The UK prime minister, who has long called for lasting peace, says this would cut support for Muslim extremism.
In an interview on the new al-Jazeera English TV channel, he told Sir David Frost it was the "most important" thing for him before he leaves office.
He said Syria and Iran could play a "constructive" role in the Middle East.
"If you are prepared to be part of the solution, there is a partnership available to you," Mr Blair said.
"But at the moment - and this is particularly so in respect of what Iran is doing in supporting terrorism throughout the Middle East and acting in breach of its nuclear weapons obligations - you are behaving in such a way that makes such a partnership impossible."
He said in Friday's interview that it was completely absurd to suggest that talking to the countries amounted to "appeasement".
'Send a signal'
Mr Blair said securing progress in the Middle East would have great "symbolic importance".
"It would send a signal to the whole of the world that this was not a battle between westerners or Christians and Muslims, but it was a battle between all those who believe in tolerance, in living together in harmony, in a non sectarian future against those who want to divide us.''
And he repeated that UK troops would remain in Iraq "for as long as the government needs us to stay".
"The reason for that is that what is happening in Iraq, as in Afghanistan, as elsewhere in parts of the Middle East, is a struggle between the decent majority of people, who want to live in peace together, and those who have an extreme and perverted and warped view of Islam, who want to create war," he said.
When Frost said the situation in Iraq had "so far been pretty much of a disaster", Mr Blair replied "it has", before adding quickly: "But you see what I say to people is why is it difficult in Iraq?
"It's not difficult because of some accident in planning.
"It's difficult because there's a deliberate strategy - al-Qaeda with Sunni insurgents on one hand, Iranian-backed elements with Shia militias on the other - to create a situation in which the will of the majority for peace is displaced by the will of the minority for war."
Mr Blair said he was against the death penalty imposed on Saddam Hussein but it was a decision for the Iraqis.
"There is something far more fundamental at stake here," he said.
"Can Iraq become a democracy in which people of different parts of the Muslim faith live together, freely?"
'Do a Hillary?'
Mr Blair was the first guest on the Frost Over the World programme on al-Jazeera International, which launched on Wednesday.
He was also asked if he would stay on as foreign secretary if the job was offered to him by his likely successor Gordon Brown.
Mr Blair said: "I think when you step down as prime minister you step down".
And he laughed at a question on whether his wife Cherie "may do a Hillary Clinton" after he has left office, and become involved in politics herself.
"No - it's a question for her but I think no," he said.