WASHINGTON — US lawmakers voted overwhelmingly Thursday in favor of ending the Pentagon's arms contract with a major Russian defense firm, with one congressman saying it was wrong to partner with "lords of war" who are supplying arms to Syria.

The amendment was adopted by a vote of 407-5, and was attached to the 2013 defense spending bill that passed the US House of Representatives and now moves to the Democrat-led Senate.

House Democrat Jim Moran, who introduced the measure, lambasted the Pentagon for its contract with Russia's state-owned Rosoboronexport, which he said sells mortars, sniper rifles and attack helicopters to Syrian President Bashar al-Assad's regime, including a shipment he said was now bound for Damascus.

The Pentagon last week announced a $171 million single-bid contract with Rosoboronexport to purchase 10 Mi-17 attack helicopters to be used by the Afghan military after US operations wind down in Afghanistan, bringing the total number of the procured airships to 33.

"I should think it's troubling to all of us that we are purchasing helicopters from a Russian firm that is directly complicit in the deaths of thousands of innocent Syrian men, women and children," Moran said on the House floor.

"We have to divest ourselves from what basically are lords of war, otherwise our condemnations of Syria's regime ring hollow."

Russia and China on Thursday vetoed a UN Security Council resolution on Syria, the third time they have blocked a measure against Damascus, sparking outrage by Western nations that had demanded sanctions against Assad.

Western powers have criticized Russia's role as an arms supplier for Damascus. Moran said Moscow sold Syria $1 billion in weapons last year.

Rosoboronexport is Russia's only arms export organization, and in June said its supplied weapons were in line with UN Security Council requirements.

More than 17,000 people have been killed since an uprising against Assad began 16 months ago, activists say.

Moran is a veteran congressman from Virginia, where US defense contractors have a substantial presence.

Also speaking out in support of the amendment was Democratic congresswoman Rosa DeLauro of Connecticut, home state of Sikorsky Aircraft Corp, a major US helicopter manufacturer.

Republican Senator John Cornyn, who sent a letter to Defense Secretary Leon Panetta in June demanding an audit of the Pentagon's contract with the Russian firm, blamed President Barack Obama's administration for failing to stand up to Moscow over the arms sales.

"The Pentagon's refusal to seek out alternatives to Rosoboronexport cements the utter disconnect between the president's stated policy in Syria and our actions abroad," Cornyn said in a statement.

The Pentagon purchased Mi-17s from Russia in part because the Afghan military was familiar with the aircraft and it would be easier to service Russian rather than American equipment once US forces leave Afghanistan in 2014.

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