MEXICO CITY, (Reuters) – Powerful drug cartels are  increasingly using gruesome videos of executions and  interrogations to intimidate their rivals, police and an  already terrified public in Mexico’s vicious drug war.

The drug gangs, battling for control of lucrative smuggling  routes into the United States, have long attached handwritten  notes to victims they dump in public as a way to scare rival  gangs and pesky state officials.

But they are now airing more and more of their dirty work  and threats on blogs or Web sites like YouTube, and bullying  Mexican media into putting their gory tapes on television for  wider play.

The aggressive media strategy raises new questions about  whether President Felipe Calderon’s war on drugs is making any  headway in weakening the gangs and in reining in a drug trade  worth up to $40 billion a year in Mexico alone.

About 28,000 people have been killed since Calderon took  office in late 2006 and sent thousands of federal police and  troops to crack down on the drug cartels.

While the gangs began using the bloody videos to send a  message to police and rivals several years ago, they have  become more common in recent months as turf wars escalate  across the country, experts and police say.

The format of the tapes is often the same: captives, many  bloodied from beatings, are tied up, blindfolded and posed in  front of a draped sheet in an anonymous setting.

Surrounded by heavily armed captors in ski-masks and guided  by questioning from an off-camera voice, the captives are  forced to confess allegiances to cartels or corrupt officials.  Many are then murdered on-camera.

The most explicit videos, when detected, are usually  removed by major web sites like YouTube but stay posted on  “narco-blogs” run by anonymous administrators.

In one video, a man with a black eye is tethered to a chair  in his underwear and appears to be strangled to death with a  tourniquet by his captors. There is a “Z” scrawled across his  chest, for Zetas, a spinoff of the Gulf Cartel.

In another video, a man is slowly beheaded with a knife.

“The message is always the same: be afraid,” said Maria  Guadalupe Licea, head of the government prosecutor’s office in  Baja California state, home to the violent city Tijuana.

Licea said the use of new technologies and media is part of  a spiraling cycle of violence in which ever more shocking  attacks inspire copycat killings.

Authorities say that the videos, while graphic, are often  little use in tracking down drug gangs.

A spokesman for Mexico’s federal police said the apparent  murders cannot be investigated until an official complaint is  raised and there is no way to prove the videos are real.

No one has been arrested yet for posting the videos. There are signs the cartels are taking their propaganda war  to a new level. In a frightening development last week, traffickers  kidnapped four journalists in northern Mexico and pressured  their employers to air 15 minutes of videos showing allegedly  corrupt police and rivals being interrogated as a condition for  release.

“It is free publicity. A company has to pay thousands of  pesos to promote their products. But for these criminal groups  … it just takes a threatening telephone call or grenades  chucked at a television station,” said Javier Oliva, a security  expert at Mexico’s National Autonomous University.