Story highlights Sen. Claire McCaskill detailed the findings of the audit in a letter sent this week to Defense Secretary James Mattis

The highlighting of issues over contractor spending comes as the Trump administration is trying to decide a path forward for the US war in Afghanistan

(CNN) A British contractor working for the US military in Afghanistan charged the government for seven luxury cars -- including Porsches, a Bentley and an Aston Martin -- and billed more than $50 million in questionable costs, according to the summary of a Pentagon audit.

The audit from the Defense Contract Audit Agency, a summary of which was released by Sen. Claire McCaskill on Wednesday, found that New Century Consulting racked up costs that included the luxury vehicles, $42,000 for automatic weapons and salaries of $420,000 to the significant others of the company CEO and CFO as executive assistants.

Sen. Claire McCaskill detailed the findings of the audit in a letter sent this week to Defense Secretary James Mattis. The Missouri Democrat wrote to Mattis asking who was in charge of authorizing the Afghanistan contract and why the contract continued after issues arose.

"Despite all of the listed issues with NCC's performance and billing practices, the Army continued to engage in contracting with NCC for sensitive work in Afghanistan," McCaskill wrote.

New Century Contracting CEO Michael Grunberg said in an email to CNN: "It would be inappropriate for us to comment on an ongoing matter." He told The Associated Press that it "is most unfair and is significantly inaccurate" to say that the executive assistants were paid inappropriate salaries.

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