WASHINGTON -- Sen. John Cornyn, R-Texas, is in the middle of a high-stakes diplomatic chess match over a Russian government-owned arms agent that supplies the U.S.-backed army in Afghanistan as well as President Bashar Assad’s regime in Syria, which the United Nations says is embroiled in a civil war against anti-government rebels.

For Cornyn, the issue is the Pentagon’s $900 million no-bid contract with Rosoboronexport – the Russian government-owned arms supplier – which he told reporters Wednesday “strikes me as profoundly wrong and inappropriate.” Russia, he said, has “blood on its hands, specifically Syrian blood.”

The senator, a member of the Armed Services Committee, has called for an investigation into the contract.

The issue of Russian support for Assad’s regime has taken center stage this week after Secretary of State Hillary Clinton spoke out against Russia sending a new shipment of attack helicopters that she said were being used to kill Syrian civilians.

“We have confronted the Russians about stopping their continued arms shipments to Syria,” Clinton said Tuesday, adding that the helicopters would “escalate the conflict quite dramatically.”

Russian Defense Minister Sergei Lavrov hit back Wednesday, saying at a news conference in Tehran that the Russians were sending only defensive weapons to Syria and, in turn, accusing the United States of arming the Syrian rebels.

The flap has placed the Pentagon in the uncomfortable position of having to defend its contract to buy helicopters for the Afghans from the same company that does business with Assad, whom the Obama administration has accused of wantonly killing civilians.

Cornyn challenged Defense Secretary Leon Panetta in a letter Monday to open the bidding for the next contract phase, sponsored an amendment in the defense authorization bill to investigate the contract and placed a hold on the nomination of the assistant secretary of the Army for acquisition, logistics and technology.

“I remain deeply troubled that the Department of Defense would knowingly do business with a firm that has enabled mass atrocities in Syria,” Cornyn said Monday. “I support the president’s call for the end of the Assad regime, as well as the goal of stopping the flow of arms to Syria. . . . But the Department of Defense’s ongoing business relationship with Rosoboronexport undermines both.”

In his weekly conference call with Texas reporters Wednesday, Cornyn said the reports of gunships going to Syria now made for “an intolerable situation” and stressed that most Americans who learn that the U.S. is doing business with an arms supplier to Syria are “aghast.”

At the Pentagon, the situation isn’t so clear-cut. While defense officials echo the Obama administration’s condemnation of the Syrian regime, they also are focused on the U.S. military’s timetable for exiting Afghanistan after more than 10 years of increasingly unpopular war. A linchpin of that strategy is arming and training Afghan forces, which historically are familiar with Russian helicopters.

The Mi-17 helicopters that the United States is purchasing for the Afghans are for transport – although they can be outfitted as gunships – and are different from the Mi-24 helicopters being supplied to Syria, which have attack capabilities.