The panel of 20 experts, who include academics and former U.S. ambassadors, warned against a military attack on Iran and called for unconditional negotiations, saying it was the only viable option to break “a cycle of threats and defiance”. “An attack would almost certainly backfire … and long experience has shown that prospects for successfully coercing Iran through achievable economic sanctions are remote at best,” they said in a joint statement to be presented to a conference on the future of U.S.-Iran relations next week.