* Newspaper suffers second grenade attack this year
* Editor says it is too risky to cover violence
* Mexico third most dangerous country for journalists
By Ioan Grillo
MEXICO CITY, July 11 (Reuters) - A newspaper in Mexico's violent city of Nuevo Laredo announced on Wednesday it will end coverage of drug-related bloodshed, one day after grenades damaged its offices for the second time this year.
Many Mexican news organizations have decided to report only basic facts about murders and massacres in recent years. But it is rare for a newspaper to drop coverage altogether.
Tuesday's attack on the daily El Manana was among the latest incidents that have made Mexico one of the world's most dangerous places for journalists.
El Manana said in an editorial that it was too dangerous to report on the execution-style murders, car bombs and decapitations that have terrorized residents in the city across the border from Laredo, Texas.
"The editorial board of the company has come to this regrettable decision because of the circumstances that we all know about and the lack of conditions to freely carry out journalism," it said.
"El Manana ... does not want to serve the petty interests of any de-facto power or criminal group," the newspaper said.
On Tuesday assailants fired at the newspaper's main offices with a grenade launcher, damaging the building but causing no injuries. A similar attack occurred on May 11.
The city south of the Rio Grande has seen a surge in violence in recent months as the brutal Zetas cartel battle rivals for control of lucrative drug smuggling routes.
In one recent incident, 14 severed heads were dumped on the street close to Nuevo Laredo's town hall in ice boxes.
Cartel gunmen across Mexico have been known to attack journalists over unfavorable coverage, as well as pressure reporters to cover mass murders they carry out.
SOCIAL MEDIA IN CROSSHAIRS
The decision will further limit the information flowing out of Nuevo Laredo, located in the major U.S.-Mexico border-trading corridor.
When a car bomb detonated in the city two days before Mexico's July 1 presidential election, there was almost no video footage or photos of the incident.
With a lack of mainstream media coverage, some have turned to social media to post information about shootouts and killings.
But the cartels have even killed people and left notes near their bodies to warn against posting on the Internet.
On Tuesday assailants also fired assault rifles and grenades at two offices of El Norte in the business city of Monterrey, a signal that a cartel may have organized simultaneous attacks against the newspapers.
No one was injured in the Monterrey attacks, the newspaper reported. El Norte is owned by Reforma, one of Mexico's most important newspaper chains.
More than 80 Mexican journalists have been murdered since 2000, according to the National Human Rights Commission, with many of those killed reporting on crime and police.
Last year Mexico was the third deadliest country in the world for journalists after Pakistan and Iraq, according to Reporters Without Borders.
There have been more than 55,0000 drug related killings and more than 6,000 disappearances during President Felipe Calderon's six-year offensive against the cartels.
President-elect Enrique Pena Nieto, who will replace Calderon in December, promises to dramatically reduce the homicide rate. (Editing by Xavier Briand)