The day after Iran celebrated the 31st anniversary of the Islamic Revolution that toppled the previous Shah's regime, there are fears of a widespread crackdown on information sources by the current government.

Three major international broadcasters have reported on Friday that jamming of their networks began the day before. They complained that Iran was broadcasting freely around the world, while denying their own people the right to receive programs from outside sources.

The BBC Persian Service, Deutsche Welle, TV and radio services, and the Voice of America have all been jammed. All three broadcast via the Hotbird satellite that covers Europe and the Middle East.

They have issued a joint statement condemning the move.

"We condemn any jamming of these channels. It contravenes international agreements and is interfering with the free and open flow of international transmissions that are protected by international treaties."

The US accused State department has accused Iran of mounting a "near-total information blockade". A spokesman has said there were strong indications that the telephone network had been taken down, SMS messages blocked, and internet communication "throttled".

The White House has announced that web giant, Google, and other internet service providers had been "unplugged" in Iran.

Reporters Without Borders said the blocking of Google's Gmail system took the drive to control cyber-space to a new stage.

A day-long security clampdown in the Iranian capital Tehran on Thursday had succeeded in preventing large-scale opposition protests as the nation commemorated the Islamic Revolution.

Opposition turnout was dwarfed by huge pro-government crowds at the state-run celebrations in the centre of Tehran, where President Ahmedinejad announced in his speech that Iran was now "a nuclear state".

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