Archbishop Desmond Tutu

Archbishop Emeritus Desmond Tutu has withdrawn from tomorrow's Discovery Leadership Summit in Johannesburg, saying he could not share a platform with former British prime minister, Tony Blair because his support of the Iraq war was "morally indefensible".

The Archbishop, a Nobel Peace Prize laureate, made the announcement on Tuesday in a statement released by his spokesman Roger Friedman.

"Ultimately, the Archbishop is of the view that Mr Blair's decision to support the United States' military invasion of Iraq, on the basis of unproven allegations of the existence in Iraq of weapons of mass destruction, was morally indefensible," the statement said.

"The Discovery Invest Leadership Summit has leadership as its theme.

Morality and leadership are indivisible. In this context, it would be inappropriate and untenable for the Archbishop to share a platform with Mr Blair."

Friedman said the Archbishop had taken a great deal of time to reach the decision. He told the New Statesman that Tutu was "a very prayerful man" who would have "spent hours on his knees considering this decision," adding as well that he did not usually make hasty decisions. "He thinks and prays and then acts. That's how he's always done things, including during the Struggle."

Mr Blair's office said he regretted the decision. In a statement, it said: "Tony Blair is sorry that the Archbishop has decided to pull out now from an event that has been fixed for months and where he and the Archbishop were never actually sharing a platform.

"As far as Iraq is concerned they have always disagreed about removing Saddam by force – such disagreement is part of a healthy democracy.

"As for the morality of that decision, we have recently had both the memorial of the Halabja massacre where thousands of people were murdered in one day by Saddam's use of chemical weapons, and that of the Iran-Iraq war where casualties numbered up to a million, including many killed by chemical weapons. So these decisions are never easy morally or politically".

Archbishop Tutu was always opposed to the war on Iraq. He said that Blair and Bush both need to examine their consciences over what happened. "If they admitted they made a mistake. If they said sorry, people would have more respect for them," he said.