Story highlights Key citizen journalist Ali Mahmoud Othman has been arrested

William Hague is "very concerned" over reports of Othman's mistreatment

Activists believe the government is torturing Othman

Kofi Annan is calling for "freedom of movement" for journalists

The Syrian government is trying to "systematically dismantle" the anti-regime "citizen journalist network" and have seized a key player in the operation, activists told CNN Saturday.

The regime has been making arrests and have seized Ali Mahmoud Othman -- instrumental in the evacuation of the wounded journalists from inside the Homs' neighborhood of Baba Amr, an activist who asked not to be named for security reasons said Saturday.

"We believe Ali is being subjected to severe torture," the activist said. "The lives of our activists and citizen journalists across the whole country are now at risk."

Activists believe that Othman, head of the media center in Homs, is being held in a secure military unit in Aleppo since his detention Wednesday. Syrian authorities have not responded to requests for comment.

Rafif Jouejati, spokesman for the opposition Local Coordination Committees, said that recently a sniper shot dead an activist hiding under a car to film columns of smoke rising from a building that had been shelled.

"Perhaps this is the regime's rationale: If they can't crush dissent using brute force, maybe killing all those who document the brute force will be effective," she said.

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Foreign news outlets have been severely limited during the government's bloody year-long crackdown against protesters. Critics say that the government has been dutifully working to stifle such independent reporting.

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U.N. envoy Kofi Annan's six-point plan to end the crisis addresses the issue. He called on the government "to ensure freedom of movement throughout the country for journalists and a non-discriminatory visa policy for them."

Amateur videographers and news reporters dubbed "citizen journalists" have braved violence to undermine the government's news coverage restrictions.

They have helped those international journalists who were able to sneak into Syria and report. And they have produced videos, photos and print reports every day that bear witness to the brutal crackdown.

Those reports have helped news outlets around the world tell the story of the violence.

Paul Conroy, a British photographer who was injured in the Baba Amr offensive, said the regime is taking steps "to ensure that independent reporting becomes impossible."

He said Othman helped him escape from Baba Amr, hammered for weeks by the military until resistance fighters retreated. Activists say other parts of the city continue to be shelled.

"After the attack and treatment of the wounded he played a significant role in assisting in our escape from Baba Amr. All our efforts must now be concentrated on saving his life. If it wasn't for him, no Western media would have been able to work in Baba Amr and bear witness to the slaughter of the civilian population," Conroy said.

The team that worked with Othman in Baba Amr is pushing for the release of Othman and other detained activists.

"We, the media office, are calling on all human rights organizations across the world, as well as the Federation of Arab Journalists and the United Nations to interfere immediately to save the life of the journalist and activist Ali Othman who is being subjected to the worst forms of torture since his arrest. We place full responsibility on the Syrian Assad regime for any harm caused to the journalist Ali Othman," said the group, known as the Baba Amr media center team.

British Foreign Secretary William Hague said he's "very concerned" about reports of arrests and torture of Othman.

"I call on the Syrian authorities to release Mr. Othman and other political prisoners immediately," Hague said in a statement.

Reporters Without Borders, the journalist watchdog group, couldn't immediately comment on Othman's situation.

But Heather Blake, the group's UK representative, said Saturday that "Syrian authorities are systematically targeting journalists working inside Syria, and particularly local journalists and the media centers that have been set up. This is based on research that we and many other organizations have done."

Another journalists' monitoring group, the Committee to Protect Journalists, says at least eight journalists have died in Syria since November, making the country "the most dangerous place for journalists in the world right now."

The latest killings occurred on Monday, when two free-lance British journalists of Algerian descent were shot and killed near the Turkish border, CPJ said. They were filming a documentary about Syrians fleeing to Turkey and were staying with activists in Idlib province.

Witness told CPJ that soldiers and militia fired at the house. State-run media "portrayed the attack as an assault on terrorists trying to infiltrate Syrian territories from the Turkish border."

The United Nations estimates that the more than 9,000 people have died since the Syrian government crackdown on protesters began in March 2011. Opposition activists put the toll at more than 10,000.