President Andres Manuel Lopez Obrador created the new security force in 2019 with a civilian command to replace federal police accused of corruption and human rights violations.

Before coming to power in 2018, Lopez Obrador had vowed to send the military back to the barracks.

But under his presidency the armed forces have kept their role tackling cartel-related violence and even gained more responsibility, including control of ports and customs and major infrastructure projects.

Lopez Obrador's National Guard reform bill was passed in the Senate by 71 votes in favor and 51 against, having already been approved by the lower house of Congress.

The ruling party argues that the military enjoys strong support and is less likely to be infiltrated by organized crime than other branches of the security forces.

But opponents are alarmed by what human rights group Amnesty International has called "the process of militarization of public security in Mexico."

More than 340,000 people have been killed in a spiral of bloodshed since the government of then-president Felipe Calderon deployed the army to fight drug cartels in 2006.

"Experience shows that today Mexico is more dangerous than 16 years ago when it was decided that the military should take to the streets," Amnesty said.

"There has been an increase in forced disappearances, arbitrary arrests, physical, psychological and even sexual torture," it added.

Lopez Obrador's opponents are expected to challenge the reform in the Supreme Court.

The government "tricked Mexicans by promising that the military would return to the barracks," said Humberto Aguilar, a legislator with the opposition National Action Party.