Mexico's biggest television network, Televisa, has cancelled a popular news programme in protest against the kidnapping of four journalists.
Media advocates said on Friday that the abductions were an escalation of a campaign by drug gangs to control information.
Four journalists - two of them from Televisa, one from Milenio Multimedia television and one from a local newspaper - were kidnapped on Monday after they left a prison in the northern city of Gomez Palacio, where they had covered a protest against the arrest of the penitentiary's director.
"We're not willing to go on the air tonight pretending nothing is happening," Denise Maerker, the anchor of Televisa's news magazine show, said.
"All the reporters of this show and all reporters run huge risks in order to do their jobs and society runs the risk of sinking into silence and disinformation."
At least one of the kidnapped journalists contacted editors and told them his safety and freedom depended on news outlets running certain pieces on the air.
"This by far opens the door to a new dangerous trend with huge ramifications for the media and society in general"
Senior Mexican journalist
Milenio promptly broadcast three unedited videos which allegedly showed policemen captured by drug traffickers who describe their links with Zetas, a rival paramilitary group that has been fighting drug cartels for control of the area known as La Laguna - chiefly the cities of Torreon, Gomez Palacio and Ciudad Lerdo.
"This by far opens the door to a new dangerous trend with huge ramifications for the media and society in general," one senior Mexican journalist, who asked not to be named, said.
"You can now expect journalists to be picked up in Ciudad Juarez, Monterrey or other major cities with the same results, because in the end no one wants to walk around with a dead reporter on our conscience."
Local media said that Hector Gordoa, a reporter from Televisa, had been freed on Thursday, although Miguel Zapata, a spokesman for the channel, said on Friday that he could not provide any information on the case.
The Televisa news network reported on Friday that a grenade exploded outside its offices in the border city of Nuevo Laredo. Some windows were damaged, but no injuries were reported.
For years, local journalists in several Mexican states have been under siege from drug traffickers and many have resorted to self-censorship to avoid being targeted.
Some drug gangs have even recruited reporters to pass the message to their colleagues on what can be covered and what needs to be ignored.
Powerful media outlets such as Televisa have found themselves in the "unacceptable situation" of being blackmailed into airing certain material to ensure the safety of the kidnapped journalists, Carmen Aristegui, a Mexican radio commentator said on Friday.
But the kidnappings of the reporters by a drug gang that demanded videos implicating alleged corrupt local officials with a rival gang be aired on national television is a new escalation in their attempts to intimidate reporters and control information, Carlos Lauria, a member of the New York-based Committee to Protect Journalists, said.
"This is unprecedented, but the truth is that for a long time there has been a battle by organised crime groups to control the flow of information," Lauria said.