The comments marked a new development in a web of corruption probes of some of the world's biggest energy traders across several countries in Latin America.

"We have found that some of these famous foreign companies were transporting contraband fuel and Trafigura's import permit has been suspended," Lopez Obrador told a regular news conference. He did not provide details.

Trafigura denied any wrongdoing in an emailed statement.

"Trafigura strongly denies that it is or has been improperly transporting and/or delivering fuel into Mexico. Trafigura complies with applicable laws and regulations in the jurisdictions in which it operates, including Mexico," it said.

"Trafigura has provided documents and evidence of compliance with applicable requirements to the relevant authorities and will continue to work with the authorities to clarify this situation."

Contraband can refer to products smuggled into Mexico or goods brought into the country under false documentation. Lopez Obrador said the attorney general's office was looking into the issue.

Mexico's energy ministry last month said four Trafigura fuel import permits were in the process of cancellation https://www.reuters.com/business/energy/mexicos-energy-ministry-suspends-several-trafigura-import-permits-2021-09-21 while one had expired.

The company previously said the suspensions were not valid and that it follows the laws and regulations of the countries where it operates.

Mexico is also probing Vitol https://www.reuters.com/business/energy/exclusive-mexico-probing-vitol-over-false-import-documents-tax-chief-2021-08-05, the world's largest independent energy trader, over "irregularities" in the documenting of its refined oil products entering Mexico that could lead to criminal charges for tax evasion.

Vitol has denied any wrongdoing, and previously said the allegations dated back a couple of years and are related to imports classified by another company with which it worked.

(Reporting by Ana Isabel Martinez and Raul Cortes, Additional reporting by Adriana Barrera; Writing by Daina Beth Solomon; Editing by Frank Jack Daniel, Dan Grebler and Richard Pullin)