The United States slapped sanctions on a Mexican judge and a former state governor on Friday, accusing them of taking bribes from traffickers and saying government corruption had allowed gangs to operate with impunity.

Santiago Nieto, head of the finance ministry's financial intelligence unit, says authorities are investigating other cases of judges allegedly taking organised crime bribes.

"I have received instructions from the president to go after anybody regardless of their position or party loyalty," he said on Monday.

The magistrate sanctioned on Friday, Isidro Avelar Gutierrez, accepted bribes from the Jalisco New Generation Cartel and the Los Cuinis Drug Trafficking Organization in exchange for favourable rulings for senior members, according to the US Treasury Department and Drug Enforcement Agency.

Asked if the case of Avelar Gutierrez was the tip of the iceberg, Nieto said it was but added he could not discuss open investigations.

"What I can say is we are working in co-ordination with various institutions of the Mexican state in cases related to corruption in the judicial system," he said.

"The Mexican financial system must not be used by criminal groups to launder money."

In December, shortly after taking office, Lopez Obrador took aim at the finances of the powerful CJNG in what Nieto described as an opening salvo in the fight to stop gangs flourishing with impunity.

Mexico's drug war has raged for over a decade since the government sent in the armed forces at the end of 2006 to crack down on cartels.

Since then, more than 200,000 people have been killed in the violence and thousands more have disappeared.

Speaking of the decision to go after Avelar Gutierrez, Nieto said: "This is a clear message. The courts are one of the central values, fundamental pillars of the democratic state. That is why if a judge or magistrate betrays that position they must be sanctioned."

Australian Associated Press