The BBC reports,

Iran offered the US a package of concessions in 2003, but it was rejected, a senior former US official has told the BBC’s Newsnight programme.
Tehran proposed ending support for Lebanese and Palestinian militant groups and helping to stabilise Iraq following the US-led invasion.
Offers, including making its nuclear programme more transparent, were conditional on the US ending hostility.
But Vice-President Dick Cheney’s office rejected the plan, the official said.
[…]
One of the then Secretary of State Colin Powell’s top aides told the BBC the state department was keen on the plan – but was over-ruled.
“We thought it was a very propitious moment to do that,” Lawrence Wilkerson told Newsnight.
“But as soon as it got to the White House, and as soon as it got to the Vice-President’s office, the old mantra of ‘We don’t talk to evil’… reasserted itself.”

Full story.