Gunmen have opened fire and tossed a grenade at a Mexican television station as it aired its nightly newscast, leaving behind a message warning the station about its coverage of drug gangs. No injuries have been reported in the attack in the city of Monterrey. Televisa Monterrey station director Francisco Cobo said the masked gunmen were in two pickup trucks and shot at the station Tuesday evening. Cobo told the El Universal newspaper the assailants left a message outside the station that read: "Stop transmitting only about us, also transmit about the narco-officials. This is a warning." The attack was the latest assault on journalists in Mexico, where drug violence has left at least 5,300 people dead in 2008.