Mexico's state oil company Pemex has banned new business with Trafigura over concerns about the commodity trader's involvement in governance and corruption scandals.

The ban will put further pressure on Jeremy Weir, the boss of Trafigura, after he pledged to introduce the highest governance standards at the secretive trading company.

The Mexican ban follows a recent decision by the Nigerian Government to prosecute Trafigura on conspiracy and theft charges. The Nigerian Economic and Financial Crimes Commission (EFCC) has charged Trafigura in relation to an oil deal in 2008, which allegedly resulted in 6.4 million tonnes of diesel being stolen.

Trafigura is one of the world's largest commodity traders and reported profits of $2 billion in the first half of this year. However, the company has been caught in several scandals in recent years, including a high-profile corruption probe in Brazil.

According to a report by Reuters, the Mexican Government has become concerned about Petroleos Mexicanos's (Pemex) exposure to companies under investigation for corruption.

As a result, PMI Commercio International, Pemex's commercial arm, imposed a ban on new business with Trafigura at the start of July. The ban is expected to stay in place for the foreseeable future, potentially blocking Trafigura from an important Latin American market.

"The world's largest independent commodity traders are facing scrutiny globally for alleged corruption after years of investigations into bribes of public officials in several countries in Latin American," Reuters said.

Trafigura told the news agency that it saw no reason for its business to be suspended in Mexico and it would be clarifying the situation at the earliest opportunity.

Trafigura's problems in Latin American and Africa come as CEO Jeremy Weir has tried to publicly defend his company's governance standards.

In a recent interview, he said: "We have a role to play in business, in society and in the industries we're developing. Ultimately what we should be doing is having best practices in that."

Weir reiterated this message in Trafigura's 2020 annual report. Weir wrote: "Earning and maintaining [stakeholders'] trust by working responsibly and engaging openly is not only a key and growing expectation; it is fundamental to our future success."

However, Weir's best practice pledge has been undermined by revelations from the criminal case against Trafigura in Nigeria.

The case was opened when a local company, Nadabo Energy, claimed that it had been duped in an oil deal. Nadabo had agreed to provide 10,000 tonnes of diesel to Mobil in 2008 and outsourced supply to a company called Mettle Energy. Mettle in turn bought the fuel from Trafigura but, when it was supplied to Mobil, about two thirds of the tonnage was missing.

Nadabo claimed the diesel had been stolen by Yusuf Yahaya-Kwande, Trafigura's agent in Nigeria. In addition to the criminal charges brought against Trafigura, other allegations have been made during the case.

Emefo Etudo, counsel for Nadabo, told the Ikeja Special Offences Court in Lagos that Trafigura had lied to the Nigerian Government about its operations in the country and that Kwande was not merely an agent but the trader's operations director.

Kwande was the "alter ego of Trafigura in Nigeria", Etudo told the court. He also claimed that Trafigura's arrangement with Kwande had helped the company evade $1.6 billion in taxes that were due to the Nigerian Government.

Trafigura has denied the charges.