That reaction has become the pretext for a crackdown by Iran's Islamic regime on mobile-phone SMS (short-message service) technology, at a time when it is hailing a breakthrough in its nuclear programme with the industrial enrichment of uranium.

According to an opposition website, the head of the country's mobile-phone company has been sacked, while four people have been arrested and accused of colluding with the Israeli foreign intelligence service, Mossad, in an official purge on text messaging.

The clampdown is in line with the authorities' uncompromising stance on the internet and bloggers. Wary of modern communications as a means of spreading political dissent, Iran is second only to China in the number of websites it filters - using, ironically, technology made in the United States.

Now, the same vigilance is being applied to texting, believed to be used by more Iranians than the seven million who use the internet.

In a disclosure that has alarmed Iranians, the regime has acknowledged monitoring text messages. This is of concern to the large number who - afraid of voicing their dissent overtly - are using biting humour in the form of text messages to belittle the government.

In a fusillade of seditious traffic, the regime's senior figures and its most sacred policies are all fair game - with Mr Ahmadinejad being a particular butt of jokes.

One joke tells of a man who has died and gone to hell, where he sees Mr Ahmadinejad dancing with the American singer-actress, Jennifer Lopez. 'Is this Ahmadinejad's punishment?' he asks. 'No,' goes the reply. 'It is Jennifer Lopez's punishment.'

Other jokes concentrate on sex, another taboo. One purports to reveal official statistics of what men do after sex: '2 per cent eat; 3 per cent smoke; 4 per cent take a shower; 5 per cent go to sleep; 86 per cent get up and go home to their wives.'

The assumption had been that this exchange of bawdy jibes and political satire could be made without detection. But now, senior police officers have announced that they are acutely aware of it and say jokes intercepted could be treated as criminal behaviour.

The government first admitted it had access to text traffic last December, when a military plane carrying more than 100 journalists crashed shortly after take off at Tehran's airport. The communications minister said text messages were kept by the government for six months, and that messages sent by those on board in the moments before the crash could be used to investigate its causes.

The first arrests over text messaging were made in the run-up to last year's presidential election, when several anti-regime student leaders were detained for urging a boycott of the poll after the regime declared voting to be an Islamic duty.