WASHINGTON (AFP) - A senior US diplomat will attend international nuclear talks with Iran on Saturday, marking a shift in US policy on negotiations with Tehran, a State Department official said.

Undersecretary of State William Burns will attend the weekend meeting in GenevaJavier Solana and Tehran's nuclear negotiator Saeed Jalili. between EU foreign policy chief

The United States has no official contact with Iran and until now has refused to even participate in preliminary discussions with Iranian officials unless Tehran first suspends its nuclear enrichment activities.

Burns, the State Department's third-ranking official, would be in Geneva "to receive the Iranian response to the latest offer of the P5 plus 1," said the official, requesting anonymity.

The meeting was planned as the five permanent members of the UN security council plus Germany seek to reach an agreement with Tehran over its atomic program, which the West believes is aimed at developing nuclear weapons.

The decision came after Washington insisted for months that it was ready to talk to Iran only if it abandons its sensitive nuclear activities, which Tehran has refused to do.

A State Department official told the Washington Post that Burns will not negotiate and will not hold separate meetings with the Iranians.

Instead, he will reiterate Washington's insistence that Iran stop its uranium enrichment operations before the US can enter into any serious negotiations.

"This is a one-time deal," the official told the Post.

The US move comes amid speculation sanctions have started to have an effect and that Iran's leadership was locked in debate about how to respond to the international offer.

Iran's President Mahmoud Ahmadinejad said on Monday that Jalili and Solana were to discuss a "timetable" for future negotiations to break the deadlock between the two sides.

"In these talks, the framework of talks and timetable of talks" will be discussed, Ahmadinejad told state television.

He also hinted at US-Iran talks without explanation: "It is possible that in the near future talks in different fields will take place with the United States."

Washington broke off relations with Tehran in 1980 in the wake of the Islamic revolution and the seizure of the US embassy. Ties have remained severed ever since amid increasing acrimony over Iran's disputed nuclear programme.

Last year, US and Iranian ambassadors broke with years of isolation and held talks focused on security in Iraq, with the nuclear issue excluded from the agenda.

There have also been reports of a possible diplomatic initiative from Washington with President George W. Bush's administration considering opening a US interests section in Tehran.

Last month the P5 plus 1 -- Britain, China, France, Germany, Russia and the United States -- presented Iran with an offer of technological incentives in exchange for suspending sensitive uranium enrichment work.

Reports say Solana is proposing to Tehran that world powers would refrain from new sanctions provided Iran did not start operating any additional centrifuges to enrich uranium.

Iran has countered with a proposal which it says will go toward solving some of the major security problems of the world, and which diplomats have described as complex.

Iran test fired a broadside of missiles in recent days -- including one whose range includes Israel -- in war games that provoked international concern.

Washington's approach towards Iran has been a major issue in the US presidential election. Democrat Barack Obama has blasted Bush for refusing to engage directly with Tehran and urged robust diplomacy while his Republican rival John McCain has branded Obama naive.