A group of 17 U.S. Senators urged on Monday the U.S. Defense Department to stop doing business with a Russian state-owned arms exporting company, which they accused of supplying arms to Syria.

In a letter to Defense Secretary Leon Panetta, the senators said that the Rosoboronexport company of Russia sold 36 fighter jets to Syria in January, in addition to arms sales last year that was worth nearly 1 billion U.S. dollars.

At the same time, the letter said that the Pentagon has agreed to purchase 21 dual use Mi-17 helicopters for Afghan military from the Russian company, in a deal worth of 375 million dollars.

The Senators, including John Cornyn, Dick Durbin, Kelly Ayotte and Kirsten Gillibrand, demanded Panetta use all available means to urge the Russians to stop supporting the Syrian government and terminate all business dealings with Rosoboronexport, which they charged as being "essentially complicit in mass atrocities in Syria."

"U.S. taxpayers should not be put in a position where they are indirectly subsidizing the mass murder of Syrian civilians," the letter said, adding that the Pentagon's business relationship with the Russian firm would undermine U.S. policy on Syria and its " efforts to stand with the Syrian people."

The U.S. and Russia have been at odds on the issue of how to end the yearlong violence in Syria, with Washington blasting Moscow for having vetoed two U.S.-backed resolutions at the United Nations Security Council to solely condemn Syrian President Bashar al-Assad's government, which insists that the unrest in Syria is the work of armed rebel groups.

Russia has made it clear that it will not pass any resolution that allows military intervention or offers support to the rebel forces in Syria, slamming the U.S. and its allies for attempting to impose a regime change similar to the one in Libya last year, where tens of thousands of people were killed by the NATO's firepower under the name of imposing a no-fly zone.