(CNN) -- South African Archbishop Desmond Tutu is withdrawing from a conference in Johannesburg to protest Tony Blair's attendance.
The Discovery Invest Leadership Summit is scheduled to start Thursday.
Tutu, a Nobel laureate, will not attend because he does not want to share a platform with Blair, said Roger Friedman, a spokesman for the archbishop. He declined to comment further on the issue.
The former British prime minister said Tutu decided not to attend because he disagrees with his support of the 2003 Iraq war.
"Obviously 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," Blair's office said in a statement posted on his website.
"As far as Iraq is concerned, they have always disagreed about removing Saddam by force -- such disagreement is part of a healthy democracy."
Groups have called for a citizen's arrest of Blair since he left office, with one website going as far as offering a reward to people who attempt to detain him.
Conference attendees include chess grandmaster Garry Kasparov and Richard Gnodde, a chief executive officer at Goldman Sachs International.