Hans Blix, the former chief UN weapons inspector, last night warned Western leaders they risked strengthening the hand of hardliners in Iran if they rush to "corner" President Mahmoud Ahmadinejad in the crisis over the country 's nuclear programme.
The man who led the hunt for the weapons of mass destruction that Saddam Hussein was accused of hiding before the US-led invasion of 2003, said it was impossible under the current inspection regime to verify the full extent of Iran 's nuclear activity or to rule out the existence of a third, secret uranium enrichment plant.
But he said a strategy of threatening and punishing Tehran without a counterbalancing attempt at persuasive dialogue would be counterproductive. "If the approach is going to be about shaming Iran and putting them in a corner and punishing them, I 'm not sure that is wise," Mr Blix told The London Independent.
He said the latest revelations had not altered the political problem of preventing Iranian nuclear proliferation. And there was a better chance of achieving the West's negotiating aims by offering the Iranians incentives than by using threats. Incentives could include investment in the civilian nuclear programme and a US offer to restore diplomatic relations in exchange for a suspension of enrichment.
"My guess is there are many different views inside Iran and the outside world should avoid strengthening the hand of the most intransigent," he said.
Israel has threatened military strikes against Iran's nuclear sites unless Washington pushes a much-tougher sanctions regime – including an embargo on petrol imports – through the UN Security Council. But Mr Blix, who denounced the Iraq war as illegal and based on flawed intelligence, said the need for constructive diplomacy with Iran was now more urgent than ever.
The key to progress he said, was to pursue the direct talks, set to open in Geneva this week. But a rush to punitive sanctions, tightened to the point where ordinary Iranians, already suffering the effects of chronic unemployment, had to endure petrol shortages or big fuel price hikes, could backfire spectacularly, he added.
"It is true that the current sanctions regime is weak and sanctions could certainly be strengthened, but if sanctions are too harsh the risk is that Ahmad-inejad, who has no legitimacy, uses a popular reaction against them to gain support," Mr Blix said. "What we need instead is a calibrated response."