Led by Sen. John Cornyn, the senators sent the letter August 5 to General Martin Dempsey, chairman of the Joint Chiefs of Staff, arguing that while Rosoboronexport, the state-run Russian arms exporter “receives huge payments from DOD [the Department of Defense], it also continues to serve as a key enabler of atrocities in Syria, transferring weapons and ammunition to prop up the bloodthirsty regime of Bashar al-Assad.”

Russia has insisted that it is fulfilling existing contracts with Syria, and that the deliveries are legal under international law. Moscow has also questioned the composition and goals of the various armed groups fighting the Assad regime.

The senators criticized the Pentagon for making US taxpayers “unwitting victims of Russian corruption” and for failing to consider “the strategic implications of sourcing mission-critical military equipment from a potentially hostile power such as Russia.”

The senators added that “[the] DOD’s preference for Russian helicopters will also make it highly difficult to achieve robust interoperability between the US and Afghan helicopter fleets, which is in the long-term interests of both nations. These problems are self-inflicted, and this policy is extremely shortsighted.”

“The department has determined that Rosoboronexport is the only viable means of meeting the Afghanistan National Security Force (ANSF) requirements” for the helicopters, Pentagon spokesman James Gregory told RIA Novosti when the controversial contract was announced.

He added that Afghan forces have already been trained to operate the Russian aircraft, and said switching to a new aircraft would require training and experience for at least three years before Afghan forces would be ready.

The letter, which was signed by seven Republicans and five Democrats, concluded with a call to end all of the Pentagon’s business dealings with Rosoboronexport.