The Iranian Foreign Ministry, meanwhile, for the first time directly accused the US of interference. It summoned the Swiss ambassador, who represents US interests in Tehran, to complain of “interventionist” statements by American officials, state-run media reported. The two countries broke off diplomatic ties after the 1979 Islamic Revolution.

US President Barack Obama said a day earlier that it would be counterproductive for the US “to be seen as meddling”. But he has also said he was “deeply troubled by the violence” in Iran and that democratic values needed to be observed. The Iranian Foreign Ministry officials, without being specific about which comments they were reacting to, expressed displeasure, the state-run IRNA news agency reported.

The protesters on Wednesday, reached by telephone, described marching silently down a major thoroughfare, some holding photographs of the main opposition candidate in Friday’s vote, Mir Hussein Moussavi. Others lifted their bare hands high in the air, signifying their support for Moussavi with green ribbons tied around their wrists. It was the fifth day of unrest since election officials declared a landslide victory for the incumbent, President Mahmoud Ahmadinejad.

Despite the government’s attempts to block communications among the opposition, calls for more mass defiance continued. In a message on a website associated with him, Moussavi called on his supporters to rally again on Thursday, and to go to their local mosques to mourn protesters killed in the demonstrations, officially numbering seven. His call directly challenged Iran’s supreme leader, Ayatollah Ali Khamenei, who had urged Moussavi to work through the country’s electoral system in contesting the election results.

The sense of threat against the opposition was growing. Reuters reported that Mohammadreza Habibi, the senior prosecutor in the central province of Isfahan, had warned demonstrators that they could be executed under Islamic law. It was not clear if his warning applied only to Isfahan or the country.

The Associated Press reported that the powerful Revolutionary Guards threatened restrictions on the digital online media that many Iranians use to communicate among themselves and to send news of their protests overseas. In a statement, the Revolutionary Guards said Iranian website operators and bloggers must remove content deemed to “create tension” or face legal action.

In Paris, Soazig Dollet, a spokeswoman for Reporters Without Borders, a press freedom advocacy group, said at least 11 reporters had been arrested.

Government officials telephoned or sent faxes to reporters in Tehran working for foreign news organisations ordering them not to venture outside to cover events being held without an official permit. That included rallies by supporters of Moussavi. At least one newspaper has stopped printing.

Defying restrictions, new amateur video surfaced outside of Iran on Wednesday, apparently showing a government militia rampaging through a dormitory area of Tehran University late Tuesday or early Wednesday.

Support for the protests came from some unusual quarters. Five Iranian soccer players, including the captain, Ali Karimi, wore green wristbands in an apparent sign of support for Moussavi at a World Cup Asian qualifying match in S Korea, the AP said.

The Fars news agency reported that the partial recount of votes ordered on Tuesday by the Guardian Council, the 12-member body of jurists which supervises elections, had begun.