In the first months of the Arab Spring, foreign journalists got well-merited credit for helping to foment and publicise popular uprisings against the region's despots. Satellite TV stations such as Al Jazeera Arabic, in particular, struck at the roots of power in Arab police states, by making official censorship irrelevant and by competing successfully against government propaganda.

Regimes threatened by change have, since those early days, paid backhanded compliments to the foreign media by throwing correspondents out of countries where they would like to report and by denying them visas to come back in. Trying to visit Yemen earlier this year, I was told that not only was there no chance of my being granted a journalist's visa, but that real tourists – amazingly there is a trickle of such people wanting to see the wonders of Yemen – were being turned back at Sanaa airport on the grounds that they must secretly be journalists. The Bahrain government has an even meaner trick: give a visa to a journalist at a Bahraini embassy abroad and deny him entry when his plane lands.

It has taken time for this policy of near total exclusion to take hold, but it means that, today, foreign journalistic coverage of Syria, Yemen and, to a lesser extent, Bahrain is usually long-distance, reliant on cellphone film of demonstrations and riots which cannot be verified.

I was in Tehran earlier this year and failed to see any demonstrations in the centre of the city, though there were plenty of riot police standing about. I was therefore amazed to find a dramatic video on YouTube dated, so far as I recall, 27 February, showing a violent demonstration. Then I noticed the protesters in the video were wearing only shirts though it was wet and freezing in Tehran and the men I could see in the streets were in jackets. Presumably somebody had redated a video shot in the summer of 2009 when there were prolonged riots.

With so many countries out of bounds, journalists have flocked to Benghazi, in Libya, which can be reached from Egypt without a visa. Alternatively they go to Tripoli, where the government allows a carefully monitored press corps to operate under strict supervision. Having arrived in these two cities, the ways in which the journalists report diverge sharply. Everybody reporting out of Tripoli expresses understandable scepticism about what government minders seek to show them as regards civilian casualties caused by Nato air strikes or demonstrations of support for Gaddafi. By way of contrast, the foreign press corps in Benghazi, capital of the rebel-held territory, shows surprising credulity towards more subtle but equally self-serving stories from the rebel government or its sympathisers.

Ever since the Libyan uprising started on 15 February, the foreign media have regurgitated stories of atrocities carried out by Gaddafi's forces. It is now becoming clear that reputable human rights organisations such as Amnesty International and Human Rights Watch have been unable to find evidence for the worst of these. For instance, they could find no credible witnesses to the mass rapes said to have been ordered by Gaddafi. Foreign mercenaries supposedly recruited by Gaddafi and shown off to the press were later quietly released when they turned out to be undocumented labourers from central and west Africa.

The crimes for which there is proof against Gaddafi are more prosaic, such as the bombardment of civilians in Misrata who have no way to escape. There is also proof of the shooting of unarmed protesters and people at funerals early on in the uprising. Amnesty estimates that some 100-110 people were killed in Benghazi and 59-64 in Baida, though it warns that some of the dead may have been government supporters.

The Libyan insurgents were adept at dealing with the press from an early stage and this included skilful propaganda to put the blame for unexplained killings on the other side. One story, to which credence was given by the foreign media early on in Benghazi, was that eight to 10 government troops who refused to shoot protesters were executed by their own side. Their bodies were shown on TV. But Donatella Rovera, senior crisis response adviser for Amnesty International, says there is strong evidence for a different explanation. She says amateur video shows them alive after they had been captured, suggesting it was the rebels who killed them.

It is a weakness of journalists that they give wide publicity to atrocities, evidence for which may be shaky when first revealed. But when the stories turn out to be untrue or exaggerated, they rate scarcely a mention.

But atrocity stories develop a life of their own and have real, and sometimes fatal, consequences long after the basis for them is deflated. Earlier in the year in Benghazi I spoke to refugees, mostly oil workers from Brega, an oil port in the Gulf of Sirte which had been captured by Gaddafi forces. One of the reasons they had fled was that they believed their wives and daughters were in danger of being raped by foreign mercenaries. They knew about this threat from watching satellite TV.

It is all credit to Amnesty International and Human Rights Watch that they have taken a sceptical attitude to atrocities until proven. Contrast this responsible attitude with that of Hillary Clinton or the prosecutor of the International Criminal Court, Luis Moreno-Ocampo, who blithely suggested that Gaddafi was using rape as a weapon of war to punish the rebels. Equally irresponsible would be a decision by the ICC to prosecute Gaddafi and his lieutenants, thus making it far less likely that Gaddafi can be eased out of power without a fight to the finish. This systematic demonisation of Gaddafi – a brutal despot he may be, but not a monster on the scale of Saddam Hussein – also makes it difficult to negotiate a ceasefire with him, though he is the only man who can deliver one.

There is nothing particularly surprising about the rebels in Benghazi making things up or producing dubious witnesses to Gaddafi's crimes. They are fighting a war against a despot whom they fear and hate and they will understandably use black propaganda as a weapon of war. But it does show naivety on the part of the foreign media, who almost universally sympathise with the rebels, that they swallow whole so many atrocity stories fed to them by the rebel authorities and their sympathisers.

Middle East correspondent for the British newspaper The Independent, Patrick Cockburn was awarded the 2005 Martha Gellhorn prize for war reporting. His book on his years covering the war in Iraq, The Occupation: War and Resistance in Iraq (Verso) was a finalist for the National Book Critics Circle Award for non-fiction.

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