MEXICO CITY, May 6 - A U.S. indictment announced last week accusing several Mexican politicians, including the governor of Sinaloa, of having drug cartel ties is triggering a rift in the ruling Morena party as factions jostle over how to respond, posing a significant challenge for President Claudia Sheinbaum.

Publicly, Sheinbaum has denounced U.S. interference and said the evidence Mexico has seen so far is not sufficient to arrest and extradite the 10 current and former Mexican officials accused by the U.S. Department of Justice of colluding with the Sinaloa Cartel to traffic drugs into the United States.

But behind the scenes, a heated dispute has broken out along pre-existing fault lines within the ruling party, three senior Morena officials told Reuters. The dispute has centered on the future of Sinaloa Governor Rubén Rocha, an influential Morena politician who said last Friday he would step down temporarily as a local investigation proceeds. He denies any wrongdoing.

Rocha is the first high-profile sitting politician to be accused by the United States of ties to drug trafficking. U.S. prosecutors have accused Mexican officials of corruption before, but only after they have left office.

The powerful faction in Morena that is loyal to former President Andrés Manuel López Obrador, the movement's founder and de facto leader, has vehemently opposed any action that could be regarded as giving in to U.S. pressure, the sources said.

That faction is led by Supreme Court Justice Lenia Batres and her brother Martí, who is in charge of Mexico’s public-sector social security agency ISSSTE, as well as Morena congressional leaders Ignacio Mier and Ricardo Monreal. The group was against Rocha stepping down, believing he should be allowed to continue in his post until allegations of cartel ties were proven in Mexico - an uncertain process that could take years to play out. They also regard any consideration of U.S. extradition as a betrayal of Mexican sovereignty. Rocha is a longtime ally of López Obrador.

On the other side of the dispute is a growing and influential group of younger leaders, headed by the party's new chie...