Mexico US border
The security certificates found in the package were being sent from the US to a Mexican company with 'global presence' (photo for representational purposes only) REUTERS/Mike Blake

Customs officials at a Mexican airport near the capital have seized $450m (£366m) in securities bonds. The large sum was being sent via a courier service under the marker "business correspondence" and was addressed to a Mexican company.

Ricardo Trevino, the customs agency administrator, did not disclose the name of the company but told a local radio channel Radio Formula that it had a "global presence". He said that the package was identified after the bonds were detected in an X-ray machine.

Trevino explained that the securities "can be cashed at any bank", and were probably linked to "tax evasion". A man involved in the operation has also been identified and is being interrogated.

AFP reported that the certificates were found as part of a global customs operation undertaken between 19 September and 10 October to detect weapons or money shipments.

Mexican airports often seize drugs or cash that can be traced to drug cartels. The authorities will now determine whether the certificates stem from legal activities, in which case the company will be penalised with a fine for not declaring their value. According to international rules, one is required to declare any amount over $10,000 at customs.

Despite a heavy crackdown by the US Drug Enforcement Administration (DEA) and Mexican agencies, drugs and money have continued to find new ways to cross the borders of the two countries. Most recently, on 18 October, Zhenli Ye Gon, a businessman who was found to be hiding US$205m in his Mexico City home was extradited by the US to Mexico where he will face charges of organised crime, drug trafficking, firearms and money laundering.

"The United States government recognised Mexico's strong interest in prosecuting its own citizen," said US Justice Department spokesman Peter Carr.