Shortly after al Qaeda gunmen stormed a giant gas plant deep in the Algerian desert last month, taking hundreds of workers hostage, their leader switched on his satellite phone to ring a journalist thousands of miles away.

"He told me 'I am Abu Al Bara and this is my number. Call me whenever you want'," said Mohamed Mahmoud Ould Aboulmaaly, editor-in-chief of the Nouakchott News Agency (ANI), a news website in Mauritania's capital on West Africa's Atlantic coast.

"After that, we spoke many times."

Aboulmaaly's exclusives on what was happening inside the In Amenas gas facility, including the raiders' demand for a halt to French air strikes on Islamist rebels in neighbouring Mali, obliged foreign newspapers and television to rely heavily on ANI during the worst international hostage-taking in recent years.

His unfettered access to the kidnappers highlighted how Mauritanian media, including ANI rivals Sahara Media and Al Akhbar, are opening a window into the shadowy world of Islamist groups operating in the vast, lawless Sahara.

An Islamic republic on the desert's western edge, bordering both Algeria and Mali, Mauritania has long wrestled with an Islamist threat within its own borders. Twice the size of France but with just 3 million people, its desert has been periodically infiltrated over the last decade by militants who have killed dozens of soldiers - and four French citizens.

Sharing their language and religion, and sometimes coming from the same tribe, Mauritanian journalists have become a conduit for Saharan jihadists to transmit their message to the world.

One of the attractions is that the country's media writes in both Arabic and French, allowing their news to penetrate directly to Western Europe. Another is that they are seen to be among the region's most independent and aggressive.

Since a 2005 military coup, Mauritania has strongly advanced in its press freedom, now far greater than Algeria's. The media watchdog Reporters Without Borders says Mauritania has the most robust press freedom in the Arab world.

While other journalists fled after the Islamists seized control of northern Mali, Sahara Media kept a correspondent in the ancient caravan town of Timbuktu, documenting how al Qaeda's north African wing AQIM imposed violent sharia law, including amputation of limbs, and destroyed sacred Sufi mausoleums.

"The Mauritanian press is seen as more open and independent than journalists in other neighbouring countries," Aboulmaaly said.

"Members of these groups have seen me speak. They were able to hear my reporting on the radio or read my articles. That is how they contacted me," he said.

For militants operating in remote desert locations, a call to a media outlet is a much faster means of disseminating their message than trying to upload a communique or video.

"The usual jihadi forums are password-protected so you have to know it to use them," said Aaron Zelin, fellow at the Washington Institute for Near East policy, who runs jihadology.net, a website monitoring Islamist activity online. "Using Mauritanian media provides a much wider audience."

The three competing websites have published a string of communiques and videos from al Qaeda-linked Saharan Islamists announcing kidnappings and executions of foreigners, becoming a central part of the groups' media strategy.

Even the Boko Haram militant group in northern Nigeria has used Mauritanian media to publish its videos.

"All these armed jihadists groups now have Mauritanian spokesmen," said Mohamed Fall Ould Oumeir, editor of the country's weekly newspaper La Tribune.

"These media have journalists from maraboutic tribes who have studied religion, sometimes even with the same guys who are now jihadists fighting in northern Mali," said Oumeir, referring to tribes led by marabouts, who are respected religious leaders in West Africa.

MET WITH BELMOKHTAR

ANI (from the French L'Agence Nouakchott d'Information http://www.ani.mr/) is owned by the private group Mauritanienne de Presse, d'Edition, de Communication et d'Impression (MAPECI), which also edits two Mauritanian dailies, Nouakchott Info et Akhbar Nouakchott, and has a radio station.

With versions in both Arabic and French, it carries mostly news about Mauritania, but also about the Western Sahara and Western Sahel region, publishing for example reports by news agency AFP on the French-led military campaign against the Islamist insurgents in Mali.

It also carries opinion pieces on Mauritanian and regional affairs and advertisements in French and Arabic.

Sahara Media also covers regional news and affairs, especially from Algeria and Morocco, in French, and has chat forums and ads as well. Its Mauritanian editor was unavailable for interview.

It is ANI's high-profile access to the jihadists that has attracted the most attention, as well as the most controversy.

After the gas field incident in which 38 hostages and 29 militants were killed, Algeria's independent newspaper El Watan, whose editor narrowly escaped two assassination attempts by Islamist radicals, denounced ANI as a "privileged channel of terrorist propaganda".

Aboulmaaly accepts he is in a unique position. He is one of a handful of reporters to have met al Qaeda's top operative in Africa, Mokhtar Belmokhtar, the one-eyed Algerian founder of the Mulathameen brigade that carried out the In Amenas attack.

He first communicated with Belmokhtar in 2011 by email and telephone, publishing a lengthy interview in which the Islamist revealed that weapons taken from Libya after Muammar Gaddafi's fall were now fuelling jihad in the Sahara. Then, last year, Aboulmaaly arranged a meeting through AQIM contacts in Mali.

He waited for two weeks before being summoned to the northern Malian town of Gao, then under rebel Islamist occupation but retaken last month along with Timbuktu by French and Malian troops.

"When I met Belmokhtar in Gao, I did not publish an interview but I learned a lot about him and his movement and how they operate," said Aboulmaaly.

Belmokhtar, who lost his left eye handling explosives on a mujahideen bomb-making course in Afghanistan, was long considered to be more of a criminal than a devout militant - making millions from cigarette smuggling and kidnapping. In recent years he has sought to ditch his reputation as "Mr Marlboro", espousing global jihad under the al Qaeda brand.

His group had carried out an attack on a Mauritanian army outpost in 2005 which killed 17 soldiers, and kidnapped Canadian diplomat Robert Fowler in Niger in 2008. But it never attempted anything as big as the In Amenas strike, led by his trusted lieutenant Abu Al Bara, who died in the raid.

"I saw a quiet man, very calm, who listens a lot and speaks with a low voice. I met him for two hours and he barely moved from his chair, sitting laid back during the whole discussion," Aboulmaaly said.

The exclusives published by ANI during the Algerian hostage-taking provided tantalising clues about direct links between the Mulathameen and al Qaeda.

The brigade, whose name means the 'Masked Ones', echoed the classic demands of al Qaeda's central leadership: the release from U.S. prisons of Omar Abdel-Rahman, the blind Egyptian sheikh jailed for a 1993 attack on the World Trade Center, and of Pakistani neuroscientist Aafia Siddiqui, whose uncle by marriage was September 11 mastermind Khaled Sheikh Mohammad.

That suggested that Belmokhtar - a former member of Algeria's Salafist Group for Preaching and Combat (GSPC) - was making good on his pledge in December to distance himself from the regional franchise AQIM, led by Abu Musab Abdel Wadoud.

"AN INDEPENDENT JOURNALIST"

With Mauritanians rising in influence among the region's Islamist cells, Belmokhtar's is not the only group with close ties to the country's media, however.

Another splinter group from AQIM, the Movement for Unity and Jihad in West Africa (MUJWA), was founded by Mauritanian Hamada Ould Mohamed Kheirou, angry at Wadoud's failure to give leadership posts in AQIM to non-Algerians.

Since then, MUJWA has used Mauritanian media to relay its messages, sending ANI a statement in September announcing it had executed an Algerian diplomat in Gao.

Aboulmaaly has been summoned by Mauritania's media regulator HAPA, which accused him of playing the hostage takers' game and damaging Mauritania's relations with Algeria.

He defended himself by saying he resisted the Islamists' request to speak live on the radio or even to broadcast live appeals from their hostages as some other media did, including France 24 and Al Jazeera.

He also refused to print the kidnappers' appeal to Algeria's army not to attack fellow Muslims.

"I asked them to tell me their message and told them we would publish it in context," he said. "For me it is simple: I am an independent journalist."

(Writing by Richard Valdmanis and Daniel Flynn; Editing by Pascal Fletcher and Sonya Hepinstall)