The Mexican government will continue to pursue La Familia drug gang which has been weakened since its leader was killed last month, a top official says.
Security spokesman Alejandro Poire said there would be no truce with the cartel, which he said was "in retreat".
His comments came as mysterious banners appeared in several cities, announcing that the gang was disbanding.
La Familia has a reputation for extreme violence but also claims to be defending family and religious values.
Banners purportedly signed by La Familia Michoacana were hung from bridges on 25 January, announcing that the gang was dissolving itself.
The signs appeared mainly in Michoacan, La Familia's stronghold, but a few were reported to have been seen in Guerrero, security consulting firm Stratfor said.
It was unclear who was behind the banners nor what the motive was. Local legislators said it could be a ploy to divert the focus of the security forces, the Associated Press news agency reported.
Mr Poire did not comment on the signs at a news conference in Mexico City, but he said La Familia had been weakened over the past two years, especially since its leader, Nazario Moreno, was killed in a gun battle with police in December.
La Familia has seen several of its key leaders arrested or killed recently.
As well as facing an offensive by the federal police in Michoacan, La Familia has also seen another drug-trafficking organisation - known as the South Pacific Cartel - move onto its turf in southern parts of the state, according to Stratfor.
La Familia is involved in cocaine smuggling to the US along Mexico's Pacific coast as well as the production of the synthetic drug methamphetamine.
The gang, which is also involved in extortion and kidnapping, often tries to present a populist view of itself as the defender of Michoacan society from attacks by rival gangs and government forces.
In 2006, La Familia came to prominence when suspected members threw five severed heads into a disco. A letter accompanying the heads declared: "Only those who deserve to die will die."
In December that year, President Felipe Calderon, who is from Michoacan, deployed troops to the state to take on the gang, later extending his drug fight to other parts of Mexico.
Since then, more than 34,000 people have been killed in drug-related violence.