The US military has been sending letters to Mali for years due to a typo, British media has reported.
The typo was rooted in similar domains: the US Army has a ".mil" domain, while in Mali, mail ends with the suffix ".ml".
According to the media, the e-mails included medical records, maps of US military installations, financial records and official travel planning documents, as well as some diplomatic messages.
Dutch internet entrepreneur Johannes Zuurbier has contacted US authorities to alert them to the leak, saying his contract with the Malian government will soon expire.
The Pentagon spokesperson responded to British media that they are aware of the situation and are taking steps to address it.
Earlier in April, the Pentagon began investigating the leak of materials to social media networks describing the state of Ukrainian troops and US and NATO plans to strengthen them.
The US media claimed that more than 100 documents could have been leaked onto the internet, and the damage caused by the incident is estimated to be significant.
In July, the Pentagon, after a massive leak blamed on an Air Force private, determined that the department needed to improve its security measures.