"Mottaki said that if they really prove this in practice ... this can be considered as a positive step," Qashqavi said.

He said that the four people still in custody were being interrogated.

Gordon Brown, the British prime minister, has called for the release of the final four staff, describing Iran's behaviour as "unacceptable, unjustified and without foundation".

Arrests 'harassment'

At the time of the arrests a day earlier, Miliband had demanded the release of the staff and described the detentions as "harassment".

In depth

The latest on Iran's post-election unrest


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The workers had been detained for their "considerable role" in riots following the June 12 presidential elections, the semi-official Fars news agency had reported.

Relations between the countries have been strained after Tehran accused Western powers - mainly Britain and the US - of inciting street protests and violence that rocked the country after the disputed polls which saw Mahmoud Ahmadinejad re-elected as president.

Britain has denied the accusations.
  
The release of the five came after country's top legislative body began a partial recount of the polls.

But Mir Hossein Mousavi, the defeated opposition candidate, has insisted the poll was rigged and should be annulled.

Fresh unrest

Iranian security forces used tear gas and batons to disperse about 3,000 people after they gathered in northern Tehran on Sunday, witnesses had said.

Police broke up the crowds outside the Ghoba mosque after they began chanting "Where is my vote?" and "Ya Hussein, Mir Hossein", linking Mousavi, the reformist candidate, to the grandson of the Prophet Muhammad.

Al Jazeera's Alireza Ronaghi, reporting from Tehran, said: "The energy on the streets doesn't seem to disappear, it just changes shape and form.

"There hasn't been any convincing statement coming from the defeated candidates ... therefore the people are still out there," he said.

Authorities had allowed the demonstration, which marked the first unrest in Iran in four days, to go ahead despite an offical ban on protests as it had officially been called to mark a bombing in 1981 that killed 70 people.

At least 20 people have been killed in a series of mass protests since Mousavi and Mehbi Karroubi, another reformist, complained that the re-election of Ahmadinejad had been rigged.