It is not clear when Straw will be visiting, nor is it known whether he will stop over in other countries.

But it will be the Foreign Secretary’s fourth visit to the Iranian capital. He is expected to stress to President Mohammed Khatami and Foreign Minister Kamal Kharazzi that they should agree to more open nuclear inspections

"The visit takes place in the context of a great deal of international concern about issues in Iran, including proliferation, human rights, terrorism, the Middle East peace process," a Foreign Office spokesman said.

"The foreign secretary will be, in part, taking that message of concern with him to Iran," he said.

Iraq's post-war reconstruction will also be on the agenda.

His last visit to Iran was in October 2002, when the US-led war to oust Saddam Hussein from power in Iraq was looking increasingly imminent.

While Prime Minister Tony Blair has backed the aggressive stance the US has taken with Iran, he would have however preferred a more conciliatory approach, analysts say.

Blair signalled a tougher line on Wednesday when he voiced support for young Iranians who took to the streets earlier this month to condemn some of the conservatives in the Iranian government.

“I think people who are fighting for freedom everywhere deserve our support,” Blair said in parliament.

Iran responded to Blair’s comments by summoning London’s ambassador to Tehran, Richard Dalton, for a diplomatic protest.

The UK Prime Minister backed  
student  protesters in Iran

In a crackdown on protests, security forces made at least 4,000 arrests across the country. Half of those arrested are still being held.

US and UK concern

It is believed that Straw discussed Iran on Friday with US National Security Advisor Condoleeza Rice. Rice has stopped in London before heading to the Middle East in coming days.

The US and UK have been concerned about Iran’s nuclear ambitions and are also pushing Russia to curb its dealings with Iran. Russia is prime supplier to Iran’s nuclear programme.

Earlier in week, Bush and EU officials demanded Iran cooperate with the UN’s International Atomic Energy Association.

Analysts say the joint statement showcased the united position both the US and EU have taken on Iran.

Admitting that Washington was prepared to act alone against Iran, Rice suggested that the US would rather see a joint position rather than the divisive sides taken on Iraq.

"If we do not want a 'Made in America' solution, let's find out how to resolve the issues of North Korea and Iran," she said, playing down however the prospect of a war against Iran.

"We do not ever want to have to deal with the proliferation issue as we did in Iraq," she told the Daily Telegraph newspaper.