Updated

A Republican senator blasted the Pentagon after it entered into a new helicopter contract with a Russian company which is supplying the Syrian regime -- even as the U.S. moves to arm the Syrian opposition.

The contract was announced Monday with Russian arms firm Rosoboronexport, for military helicopters that will go to Afghan security forces. The Pentagon argues the helicopters are the only option, but Sen. John Cornyn, R-Texas, is adamant that the U.S. find an alternative considering the company's ties to the Bashar Assad government in Syria.

"American taxpayers should not be indirectly subsidizing the murder of Syrian civilians," Sen. John Cornyn, R-Texas, said in a statement.

Cornyn first challenged the Pentagon over a prior contract with Rosoboronexport last year, and was able to successfully pass an amendment in November barring the use of funds for contracts with the company.

But the latest contract used money from the fiscal 2012 budget, which was approved before Cornyn's amendment.

More On This...

    Cornyn said Tuesday that the Obama administration also could get around that amendment by arguing the contract was in the country's national security interests.

    "In other words: they want us to believe that we are promoting U.S. security by doing business with a Russian arms dealer that is helping an anti-American, terror-sponsoring dictatorship commit mass atrocities," he said.

    The $572 million contract announced Monday would purchase 30 Mi-17 helicopters for Afghan security forces, which deals with counterterrorism and other missions. The contract also includes spare parts, test equipment and engineering support services. The contract lasts through the end of 2014.

    The Pentagon has defended its arrangements with Rosoboronexport, arguing that the Mi-17 helicopters are "uniquely suited" for Afghanistan.

    Spokeswoman Maureen Schumann said Wednesday the Russian government has notified the U.S. that Rosoboronexport is the "sole legal exporter of Mi-17s for military use."

    "The department explored whether there were any alternatives to contracting with Rosoboronexport to meet this requirement, but none were identified," she told FoxNews.com.

    Gen. Joseph Dunford, commander of the International Security Assistance Force in Afghanistan, also said Tuesday that the Mi-17 is favored in part because of its "simplicity."

    "I can tell you, having watched them very closely here over the last several months, the Mi-17 is actually operating very well for the Afghans. It seems to be going through their operational construct and they seem to be using it very effectively, both for casualty evacuation, to move troops around the battlefield, and in fact, this week we've just equipped it with a weapons system, so it's also now capable of providing some limited fire support," he said.

    The contract comes as U.S. forces look to hand security responsibility in Afghanistan over to the Afghans.

    As for the company's work with Syria, Russia's government has claimed the company's arms cannot be used against Syria's civilian population.

    "Weapons do not shoot all by themselves. It is people who shoot from them. Unlike its partners, Russia has never tried to add oil to the fire," a Russian official was quoted as saying last year.

    But Human Rights Watch claimed last year that Rosoboronexport nevertheless appears to be Syria's main weapons supplier, questioning how the company tracks how its weapons are being used.

    The Pentagon contract comes at a vital time, as the Obama administration steps up its support for the anti-Assad opposition by pledging to provide small arms to certain opposition groups. The contract potentially puts the U.S. government in the uncomfortable position of funding a company that is aiding the other side of that civil war.

    Despite Russia's claims, a Pentagon official wrote a letter to Cornyn in March 2012 that acknowledged "evidence" that Rosoboronexport's arms "are being used by Syrian forces against Syria's civilian population."