Bayeux (France) (AFP) - Kidnappings, beheadings, a hatred of journalists: the areas controlled by the Islamic State group in Iraq and Syria have become "black holes" of news where even war-hardened reporters dare not venture.

Speaking on the sidelines of the annual Bayeux-Calvados awards for war correspondents in northwestern France, where three of seven prizes went to coverage of the conflict in Syria, journalists used to danger zones said reporting on areas overrun by jihadists had become near-impossible.

"We don't know what is going on in Fallujah, in Ramadi, in Mosul. These are big (Iraqi) cities," said Jean-Pierre Perrin, a reporter for Liberation daily.

"It's a war without witnesses."

Jihadists from the radical IS group launched a lightning offensive in northwestern Iraq in June and seized the second biggest city Mosul before sweeping across much of the Sunni Arab heartland.

They also control large parts of conflict-ridden Syria, and have not only executed locals who stand in their way but also beheaded American and British journalists and aid workers -- to global outrage.

- Journalist 'a prey' -

As a result, even seasoned war reporters are refusing to go anywhere near the areas where IS operates.

Photographer Laurent Van der Stockt, who has received several prizes in the past for his reports in Syria and is known for his contacts on the ground, has said he will not venture into IS-held territory.

Jean-Philippe Remy, a journalist for Le Monde daily who travelled to Syria in 2013 with Van der Stockt, said deciding to stay away felt like a "failure".

"It becomes wickedly complicated when a journalist becomes a prey or... part of a propaganda machine."

Christophe Deloire, head of Reporters Without Borders, said IS kept part of its "myth" going thanks to violence against journalists and general mystery about what goes on in the areas it controls.

As a result, the conflict can "unfortunately only be covered using indirect sources."

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Jon Randal, a globetrotting journalist who spent 30 years at the Washington Post and was this year's jury president, said he was "very pessimistic."

"Not only can we not go there but these radical groups have mastered all types of modern media and social networks," he said of the ability by IS jihadists to use the Internet to spread their message and recruit candidates.

Journalist Medyan Dairieh did spend three weeks embedded with IS to report on the group's self-proclaimed caliphate for Vice News, but the documentary stirred controversy.

"It's propaganda," said Van der Stockt.

"We're verging on activism. Sometimes it looks like IS itself filmed," he added.

- 'Ideological shift' -

Reporters Without Borders stressed that "black holes of information" were not a first, pointing to no-go or hard-to-access zones such as Eritrea, Pakistan's restive Baluchistan province or parts of Afghanistan.

But "there has been an ideological shift," said Perrin, who started covering Afghanistan at the time of the Soviet war in the country.

"Travelling with Mujahideen was no different in terms of risk from any war situation: you could be killed by the Soviet army, step on a landmine or be victim of a bombing.

"But it didn't necessarily involve being kidnapped, beaten up, tortured and executed. They didn't see journalists as enemies."

Remy, meanwhile, said the current situation with IS was similar to what took place in Somalia.

"There was a first phase when there was a lot of danger, but acceptable danger, such as thuggish war chiefs who shot their guns for any old reason," he said.

"But when an ideological dimension was added to this and Shebab (Islamist militants) started to spread out, they said: 'We only want to talk to journalists who are preferably Somali, Muslim and whom we have known for a long time'.

"From then on, that was it. There are no longer any in-depth articles for this reason."