MEXICO CITY -- Prosecutors in the western Mexican state of Jalisco asked the public Tuesday to ignore banners hung around the city that were purported to be from the cartel that killed 15 state police officers in an ambush last week.

The banners signed with the initials of the Jalisco New Generation cartel said that the cartel's problem is not with the citizens, but rather with kidnappers and rival gangs.

In an unusual move, the state prosecutor's office responded to the banners through its official Twitter account on Tuesday. It asked the public to ignore them, attributing them to the group that killed 15 state police officers and "now looks to generate empathy with citizens."

Such banners are a common method for cartels to convey messages to the public. Sometimes they are threats and others seek to distance the cartel from a violent act. Authorities rarely acknowledge them.

Speaking to reporters, Jalisco state attorney general Luis Carlos Najera, said the banners were under investigation.

"These people continue poisoning the youth, continue stealing hydrocarbons, continue attacking authorities; they cannot say that they don't want to harm society," Najera said.

On April 6, gunmen stopped a police convoy on a rural highway and opened fire, killing 15 people and wounding five. It was the bloodiest single attack on Mexican authorities in recent memory.

One week earlier, cartel gunmen attempted to assassinate the state security commissioner and on March 19, they killed five federal police officers. The security commissioner had said the attacks were revenge for state forces killing a cartel leader.

The U.S. government considers Jalisco New Generation one of the most powerful drug trafficking organizations in Mexico, operating in at least seven Mexican states, as well as the United States. The U.S. Treasury Department announced sanctions against the cartel last week, placing it on the U.S. Foreign Narcotics Kingpin list.