Thirteen major news organisations, including AFP, have called on the leadership of Syria's rebels to ensure journalists working in opposition areas can do so free from the threat of kidnap.
"We believe it is imperative for the leadership of the armed opposition to commit itself to assuring that journalists can work within Syria, secure from the threat of kidnapping," said the organisations in a letter published Wednesday.
"Among other things, we ask the leadership to assist in identifying those groups currently holding journalists and take the steps necessary to bring about their release," it said.
The letter was addressed mainly to the Free Syrian Army's command, as well as to the Islamic Front, a large alliance of Islamist factions formed late last month.
Rights groups describe Syria as the world's most dangerous country from which to report.
Twenty-five journalists have been killed in Syria since the start of the conflict in March 2011, according to Reporters Without Borders (RSF). The news organisations estimate that more than 30 journalists are being held.
Among the missing is AFP contributor US freelancer James Foley, who was seized by armed men in the northern province of Idlib in November last year.
On Tuesday, the families of Spanish freelance photographer Ricardo Garcia Vilanova, who has also contributed to AFP, and El Mundo's Middle East bureau chief Javier Espinosa made a public appeal to the Al-Qaeda-affiliated Islamic State of Iraq and the Levant (ISIL) for their release.
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The pair went missing on September 16 in Tal Abyad in northern Syria.
ISIL is believed to be holding several other foreign journalists, as well as scores of Syrian activists.
"We understand that, as in any war zone, reporters face great risk of injury and death, and we accept those risks, but the risk of kidnapping is unacceptable, and the leadership is in a position to reduce and eliminate that risk," said the statement.
Scores of foreign journalists have crossed borders illegally into rebel-controlled zones to cover the Syrian conflict.
But the rising threat of kidnapping, mostly by jihadists, has made news organisations limit their coverage from rebel areas.
"The international news organisations signing this letter are committed to providing the world with fair and in-depth coverage of the war, the activities of rebel-aligned forces, and the suffering of civilians within Syria," said the letter.
"Those stories can only be told if journalists have the ability to travel within Syria without fear that they will be victims of kidnappings by criminal gangs or groups associated with the rebels," it said.
The statement also said the news organisations "ask the leadership to assist in identifying those groups currently holding journalists and take the necessary steps to bring about their release".
The letter was signed by news executives from AFP, AP, Atlantic Media, BBC News, The Economist, Getty Images, The Guardian, The Los Angeles Times, The New York Times, Reuters, The Telegraph, The Wall Street Journal and The Washington Post.