The interim government in Iraq closed the satellite broadcaster on Saturday for one month after alleging it encouraged criminals and gangsters.
The Iraqi authorities have accused the station of fuelling the wave of kidnapping of foreign workers by regularly screening tapes issued by the hostage-takers.
Joel Campagna, a co-ordinator at the Committee to Protect Journalists, said: "The closure is a serious blow to press freedom in Iraq and what Iraqi officials should do is engage with channels they disagree with rather than censor them."
He added: "Viewers lose out and the credibility of the interim government, as one that supports the principles of press freedom, is undermined."
The US government has not said it supports the move, although it has been critical of Al Jazeera in the past. Donald Rumsfeld, the defence secretary, has accused the station of lying.
Adam Ereli , a US state department spokesman, told reporters in Washington: "We are all trying to work to get the balance right, to get the balance between respecting the free and independent media and acting against insurgents and providing for security."
Al Jazeera has not enjoyed a good reputation among the establishment in the West following the war in Iraq, where it was condemned by London and Washington for biased reporting and screening images of dead and captured coalition troops.
It has been claimed that the channel was infiltrated by Iraqi intelligence agents in May last year as part of an effort to subvert the network's coverage. The allegations were made after documents were discovered in Baghdad claiming that the Iraqi secret service controlled as many as three agents working for Al Jazeera.
The station made its name covering the war in Afghanistan when it broadcast an interview with Saudi terrorist Osama bin Laden.
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