They were handing out the photocopies by the thousand under the plane trees in the centre of the boulevard, single sheets of paper grabbed by the opposition supporters who are now wearing black for the 15 Iranians who have been killed in Tehran – who knows how many more in the rest of the country? – since the election results gave Mahmoud Ahmadinejad more than 24 million votes and a return to the presidency. But for the tens of thousands marking their fifth day of protests yesterday – and for their election campaign hero, Mirhossein Mousavi, who officially picked up just 13 million votes – those photocopies were irradiated.

For the photocopy appeared to be a genuine but confidential letter from the Iranian minister of interior, Sadeq Mahsuli, to Iran's Supreme Leader, Ayatollah Ali Khamenei, written on Saturday 13 June, the day after the elections, and giving both Mr Mousavi and his ally, Mehdi Karroubi, big majorities in the final results. In a highly sophisticated society like Iran, forgery is as efficient as anywhere in the West and there are reasons for both distrusting and believing this document. But it divides the final vote between Mr Mousavi and Mr Karroubi in such a way that it would have forced a second run-off vote – scarcely something Mousavi's camp would have wanted.

Headed "For the Attention of the Supreme Leader" it notes "your concerns for the 10th presidential elections" and "and your orders for Mr Ahmadinejad to be elected president", and continues "for your information only, I am telling you the actual results". Mr Mousavi has 19,075,623, Mr Karroubi 13,387,104, and Mr Ahmadinejad a mere 5,698,417.

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Could this letter be a fake? Even if Mr Mousavi won so many votes, could the colourless Mr Karroubi have followed only six million votes behind him? And however incredible Mr Ahmadinejad's officially declared 63 per cent of the vote may have been, could he really – as a man who has immense support among the poor of Iran – have picked up only five-and-a-half million votes? And would a letter of such immense importance be signed only "on behalf of the minister"?

The letter may well join the thousands of documents, real and forged, that have shaped Iran's recent history, the most memorable of which were the Irish passports upon which Messers Robert McFarlane and Oliver North travelled to Iran on behalf of the US government in 1986 to offer missiles for hostages. The passports were real – and stolen – but the identities written onto the document were fake. Mr Ahmadinejad's loyalists will undoubtedly blame "foreigners" for the "letter" to Ayatollah Khamenei. But its electrifying effect on the Mousavi camp will only help to transform suspicion into the absolute conviction that their leader was quite deliberately deprived of the presidency. Marjane Satrapi, the acclaimed author and the Oscar-winning director of the black and white cartoon Persepolis, was in Brussels brandishing the same document.

In Tehran, there must have been five or six thousand Iranians wearing black, many of them carrying this toxic document in their hands, although they were far fewer than Monday's million-strong march and scarcely a fifth of their number reached Azadi Square from the centre of Tehran. Their enthusiasm to maintain their protest – led yesterday by a cavalry of a hundred or more motorbike riders – was cruelly treated by the organisers, who clearly had little idea whether they were supposed to direct them to a central venue or all the way out to Azadi. At times, they stood in the heat for more than a quarter of an hour while organisers argued about the route. This was no way to overthrow a government.

What was significant, however, was that once more the security authorities chose not to confront the Mousavi demonstrators. Military conscripts wearing bright yellow jackets and standing with their hands clasped behind their back – rather than holding batons – lined the first mile of the road but then abandoned the marchers to their own devices. This followed less than 24 hours after the frightening confrontation between up to 20,000 Mousavi and Ahmadinejad supporters at Vanak Square on Tuesday night when Iranian special forces paramilitary police protected Mr Mousavi's men and women from the government "Basiji" militia. Although some civilians were later hurt in fist-fights on the street, the government cops brought in reinforcements and prevented the Basiji and thousands of other Ahmadinejad supporters from entering north Tehran.

Mousavi was clearly behind yesterday's half-hearted march, for he issued a statement to the participants, condemning those who killed seven men in the dormitories at Tehran University on Sunday night "and beat boy and girl students and killed people in Azadi Square". He sympathised, he said, with these "martyrs" and urged all Iranians to send their condolences to the families of those who had been killed.

The highly dubious election results, however, are arousing concern far outside Mr Mousavi's millions of voters. Fifty-two MPs have asked the interior minister why he could not prevent the post-election intimidation and violence. Parliament has asked for a fact-finding investigation into the vandalisation of Tehran University property. Ali-Akbar Mohtashemi, a member of the Combatant Clerics Assembly – an important figure who founded the Iranian Revolutionary Guards and sent them to Lebanon when he was Iran's ambassador to Damascus – has demanded a committee to investigate the election results, made up of senior clerics, MPs, members of the judiciary, the Council of Guardians and an official of the interior ministry.

But suppression of the free speech which Mr Mousavi's loyalists demand so insistently continues. Yesterday morning, a 26-year-old student doing his doctorate at Oxford, Mohamed Reza Jaleopour, son of a professor at Tehran University, was arrested without charge at Tehran airport. The pro-Mousavi paper Green Word was again closed down.

As for Mr Mousavi, it seems that, once broken, the "mind-forged manacles of fear" are difficult to re-attach. But revolutionary governments are tough, steely creatures with sharp claws, and the Ahmadinejad regime is not about to collapse.

Interior Ministry's letter to the Supreme Leader

Salaam Aleikum.

Regarding your concerns for the 10th presidential elections and due to your orders for Mr Ahmedinejad to be elected President, in this sensitive time, all matters have been organised in such a way that the results of the election will be in line with the revolution and the Islamic system. The following result will be declared to the people and all planning should be put in force to prevent any possible action from the opposition, and all party leaders and election candidates are under intense surveillance. Therefore, for your information only, I am telling you the actual results as follows:

Mirhossein Mousavi: 19,075,623

Mehdi Karroubi: 13,387,104

Mahmoud Ahmadinejad: 5,698,417

Mohsen Rezai: 38,716

(signed on behalf of the minister)

Day 5 of Iran crisis

Political football

Iran's World Cup qualifier against South Korea in Seoul yesterday took on a decidedly political flavour. At least five of the Iranian team sported green bands around their arms or wrists – the signature accessory of Mousavi supporters back on the streets of Tehran – in an apparent protest against the disputed election back home.

But after half-time, some had removed the impromptu additions to their kit, prompting speculation they had been ordered to do so by their coach. The captain Mehdi Mahdavikia seemed to defy the team edict, much to the delight of fans waving banners with the plea "Free Iran" and chanting "Go to Hell Dictator". The game ended 1-1.

Ambassadors berated

Diplomatic relations frayed as the government summoned an ensemble of Western ambassadors to complain about interference. According to Iranian state TV, Tehran accused Washington of "intolerable" meddling in its internal affairs, the first time it has blamed the US for playing a role in the post-election turmoil. Barack Obama took pains to note there was little difference between Ahmadinejad and Mousavi. "Either way we are going to be dealing with an Iranian regime that has historically been hostile to the United States," he said. Britain's ambassador was berated for the recent comments of Gordon Brown and David Miliband, as well as the BBC's news coverage of the crisis. France, Germany and Italy were also given a talking to.

Missing persons

The International Campaign for Human Rights in Iran reported that scores of notable figures had been arrested and their whereabouts unknown. These included Saeed Hajarian – a one-time adviser to the reformist president Mohammed Khatami – who sustained brain and spinal injuries in a failed assassination attempt nine years ago, and as such needs constant medical attention. Also arrested was Mohammad Ali Abtahi, a senior adviser to Mehdi Karroubi who came in third in Friday's presidential election, according to the official results. Mohamed Reza Jaleopour, the son of a reformist university professor, was also detained at Tehran airport as he prepared to fly to England where he is studying for a PhD at Oxford University.

Regime splits

It emerged that the daughter of Hashemi Rafsanjani, the head of the influential Assembly of Experts that has the right to dismiss the Supreme Leader, had attended Tuesday's opposition rally. Faezeh Rafsanjani's public display of support for Mousavi, in defiance of a ban on unauthorised marches from the interior ministry, was widely interpreted as another sign of high-level rifts in the Islamic Republic. Meanwhile Mousavi has declared today a day of mourning, urging Iranians to come together in mosques or congregate peacefully on the streets. "A number of our countrymen were wounded or martyred," he said on his website. "I ask the people to express their solidarity with the families."

Bloggers threatened

Iran's Revolutionary Guards, the country's most powerful military force, made its first pronouncement on the post-election crisis, warning that the country's bloggers must remove any materials that "create tension" or face legal action. It marked another escalation of the information crackdown. But graphic images and detailed updates continued to leak out over sites such as Twitter, although the traffic directly from Iran appeared fractionally lighter than in previous days.