MEXICO CITY A powerful faction of the Sinaloa cartel led by the sons of ex-Mexican drug lord Joaquin "El Chapo" Guzman has banned fentanyl production and sales in Sinaloa, according to roadside banners, though analysts doubted the group would leave such a profitable business.

The banners that appeared in the northern Sinaloa state on Monday, known as "narcomantas", were signed by Los Chapitos, a grouping of brothers who took over their father's criminal empire when Guzman was extradited to the United States in 2017.

It is unclear who put up the banners, festooned to bridges and overpasses. They appeared at a time when U.S. authorities are ramping up pressure on Mexico to take action against crime groups involved in fentanyl production.

The U.S. government this year portrayed Los Chapitos, or "little Chapos", as the principal providers of fentanyl into the United States. Last month, Ovidio Guzman, the youngest of the four Los Chapitos brothers, was extradited to the United States.

"The sale, manufacture, transportation or any type of business involving the substance known as fentanyl is strictly prohibited in Sinaloa," the banners said.

Leo Silva, a former U.S. Drug Enforcement Administration (DEA) agent who worked in Mexico, said the banners were likely an attempt by Los Chapitos to shift the blame for fentanyl production on to others.

"Coupled with extradition of one of the brothers, it's a ploy to take the heat off of them," Silva said. "I don't see them stopping production."

In July, Sinaloan investigative outlet Riodoce reported that Los Chapitos had told producers in Culiacan, the state capital, to stop manufacturing fentanyl. Soon afterwards, bodies were discovered of men who had been tortured and had fentanyl pills dumped on them, in an apparent signal to others.

It was also not clear if Los Chapitos could enact such a ban across Sinaloa, as much of the territory is controlled by El Chapo's old partner, Ismael "El Mayo" Zambada, who runs another powerful grouping of the cartel.

Silva doubted Los Chapitos would stay away from fentanyl.

"It's too much money to turn down or turn their back on," he said.

(Reporting by Drazen Jorgic; Editing by Jamie Freed)