(CNN) -- The Televisa TV station in Monterrey, Mexico, came under attack Tuesday night from hooded gunmen who launched a grenade and fired at least one high-power weapon at it, federal authorities said.
No one was wounded or injured, the Mexican attorney general's office said, but local newspapers reported that a woman suffered a "nervous attack."
Officials did not say who launched the 8:55 p.m. drive-by attack during the station's prime newscast, though news outlets said narcotics traffickers were responsible.
The attackers left a note telling the TV station, a CNN affiliate, to quit reporting solely on organized crime and to start broadcasting news on government officials involved in the drug trade, said the milenio.com news site and El Porvenir daily newspaper.
The message was left on the rear of a Volkswagen parked nearby and said in part: "Stop transmitting only about us, also transmit about the narco-officials," El Porvenir said.
At least one TV station official received a similar threat in a telephone call a few hours before the attack, El Porvenir said.
Televisa said in a broadcast shortly after the attack that it will not be intimidated.
Federal authorities said they are investigating.
The grenade damaged a parking lot, and the gunfire struck an outside wall of the station. Video footage on Televisa and TV Azteca showed four bullet holes high on a wall and a spent shell casing on a sidewalk.
Nuevo Leon state authorities said they found at least nine shells from a .40-caliber weapon, commonly called a "matapolicias" -- Spanish for "police killer." Televisa news director Francisco Cobos said there were at least 12 bullet holes, El Excelsior newspaper reported.
Police said Wednesday one of the handguns believed used in the attack was found inside an abandoned red Pontiac parked in front of an elementary school, according to milenio.com. A pair of black pants and a blue sweatshirt also were found inside the car, which had a Texas license plate, the news site said.
Attacks on journalists are not rare in Mexico.
"The violence perpetrated by drug traffickers has reached a new and terrifying level in Mexico," said Latin American scholar Robert Pastor, a former National Security adviser to President Carter and now a professor of international relations at American University in Washington.
"Kidnappings, beheadings and other violence is at a scale that Mexico and few civilized nations have encountered before. Journalists are caught in the middle of that. They're targets."
The Committee to Protect Journalists said Mexico is "one of the most dangerous countries for the press." Reporters Without Borders agrees, saying Mexico "is still the most deadly in the Americas for journalists."
Carlos Lauria, CPJ's senior coordinator for Latin America, said Wednesday that the attack on the TV station shows that "journalists covering the war on narco-traffic are in the line of fire."
Since 1992, the journalists' group said, 14 journalists have been slain in direct relation to their work and another 18 killed under unclear circumstances in Mexico.
The organization lists one Mexican journalist killed in 2008 in connection with organized crime. Radio reporter Alejandro Zenon Fonseca Estrada was shot to death in September when he was hanging anti-crime posters on a major street in Villahermosa, the capital of the Gulf Coast state of Tabasco. A drug cartel member was arrested and charged in the slaying, police said.
Four other journalists were killed in Mexico last year, two of them crime reporters, the journalists' committee said in its latest report. Another crime reporter disappeared in 2008, but his body has not been found, the CPJ said.
The violence has a chilling effect on journalists, who may be afraid to cover the drug war, said the CPJ's Lauria.
"Lamentably, Mexico has been unable to guarantee even minor levels of safety," he said Wednesday. "All this violence produces much fear. Without strong government action, that leads to fear and auto censoring."
Drug-fueled violence reached record levels in Mexico last year, with around 5,400 slayings in 2008, more than double the 2,477 reported in 2007, Attorney General Eduardo Medina Mora said last month.
More than 10 slayings already have been registered in the first week of the new year.
A 44-year-old businessman was gunned down while jogging in a Mexico City park Monday. Robbery apparently was not a motive, as the man's wallet, large sums of cash and other valuables were not taken.
That same day, a man's bullet-riddled body was found in a garbage can in Ciudad Juarez, on the U.S. border. A message attached to the container mentioned a local drug cartel.
Over the weekend in the same area, officials found three bodies, including the charred remains of a woman floating in a pond and the beheaded and dismembered body of a man in a ditch.
Monterrey, where the Televisa attack took place, is the capital of the state of Nuevo Leon in northeastern Mexico. It's considered one of the most important cities in the nation, with a metro area of about 4 million people.