President Bush's decision to send William Burns, his third-ranking diplomat, to observe nuclear negotiations in Geneva with Iran, represents a long-overdue shift in American policy - underlined by plans revealed in yesterday's Guardian to re-establish a diplomatic presence in Tehran. Hitherto, the US had demanded that Iran must concede the main point of negotiations, namely suspension of its uranium enrichment programme, before talks begin. Iran has responded positively to negotiations, but ruled out the US precondition of suspension. The US still states that it will only enter into dialogue with Iran if it halts its enrichment programme.

Iran's nuclear plants are all under the safeguards of the International Atomic Energy Agency, which has stressed consistently that there has not been any illicit diversion of declared nuclear material. Despite no evidence of a nuclear weaponisation programme, the US pressured the member states of the governor's board of the IAEA to report Iran's file to the UN security council in February 2006. Three rounds of resolutions and sanctions followed.

The Bush administration's policy towards Iran was inspired initially by its quick success in regime change in Iraq. It has pursued the dual strategy of demonising, isolating and pressuring Iran while trying to destabilise the country by covert operations in order to prepare the ground for a military attack.

However the hawks, led by Dick Cheney, have failed to make any headway. In December 2007, the National Intelligence Estimate reported with high confidence that Iran does not have a military nuclear programme, disarming the principal allegation against it. For a time, a concerted attempt was made to create a casus belli by accusing Iran of arming the militants who are "killing our soldiers" in Iraq. But no real evidence for this charge was ever produced, the Iraqi government refuted it and the allegations have not been trumpeted by the US in recent months.

In Iran itself, the US pressures have backfired and radicalised large sections of the population - including those opposed to the government - in defence of Iran's rights under the non-proliferation treaty. According to public opinion surveys, the overwhelming majority has supported the government in resisting pressure to halt enrichment.

These failures of US policy coincide with the high sensitivity of the price of oil, the background to a recent report by the Rand Corporation for the American air force warning against any military attack or inflaming ethnic tensions and proposing reconciliation with Tehran.

While the positive shift in policy is a setback for them, the hawks are by no means defeated. We have been in this position before. The US and Iran had three rounds of negotiations about stability in Iraq last year, which only led to a new hype in US accusations against Iran. On Monday, Israeli military adviser Amos Gilad said that Israel is preparing to attack Iran if diplomacy fails, and that the US would not veto it. Investigative journalist Seymour Hersh has warned of an October surprise - a massive US bombing campaign in Iran - triggered by a "Gulf of Tonkin" incident to boost McCain's electoral chances if Obama maintains his lead in the opinion polls.

In this volatile state, the international peace movement should multiply its efforts to avert war in the remaining six months of Bush's term. The resolution in Congress for what amounts to a naval blockade of Iran is, in effect, an act of war. The EU and the international community should call for the military option to be ruled out, and for the US to drop its precondition and enter into direct, comprehensive negotiations with Iran.

· Abbas Edalat is the founder of the Campaign Against Sanctions and Military Intervention in Iran

campaign@campaigniran.org