Lawmakers urged Secretary of State John Kerry to "send Russia a clear message" that the United States will not tolerate Moscow’s arming of the Iranian regime.
The lawmakers wrote to Kerry on Thursday evening following reports this week that Russia will arm Tehran with five advanced S-300 air defense systems, a weapon that would significantly increase Tehran’s military capabilities and potentially embolden its allies, Hezbollah and Syria.
"This potential arms transfer would have devastating implications for Middle East regional security," Reps. Ted Deutch (D., Fla.) and Peter Roskam (R., Ill.) wrote to Kerry, expressing their "deep concern" over the matter.
Senior Russian and Iranian officials were scheduled to discuss the arms deal on Friday, according to Iranian media reports.
"Maintaining a credible military threat is a crucial component of United States policy to prevent Iran from obtaining nuclear weapons capabilities," the lawmakers wrote. "If the S-300 enters into service in Iran, it would significantly expand the military effectiveness of Iranian air power, which will only embolden Supreme Leader Ali Khamenei’s illicit pursuit of nuclear weapons."
The letter was sent to Kerry as he entered into a series of meetings with his Russian counterpart on how to deal with Syria and its contested chemical weapons stockpile.
Roskam and Deutch asked in the letter that Kerry not back down from also addressing the thorny issue of Russian arms deals with Iran, which have historically been a sticking point between the two nations.
"While we understand the role that diplomacy with Russia could play in potentially forcing Syria to abandon its chemical weapons, we ask that you remain steadfast in your opposition to the transfer of destabilizing weapons to Iran and other rogue nations in your upcoming discussions in Geneva," the letter states. "Failure to pressure Russia on this issue may allow Iran to obtain capabilities that would materially diminish the credibility of a U.S. military threat."
Russia’s potential arming of Iran damages America’s credibility on the international stage, Roskam told the Washington Free Beacon.
"Russia should immediately address reports that it plans to sell advanced S-300 anti-aircraft systems to Iran—one of the world's largest state sponsors of terrorism," Roskam said.
"These systems would significantly bolster Iran's air defense capabilities and compromise the integrity of a credible U.S. military threat," Roskam said. "We must continue to stand up against these dangerous and provocative acts, which threaten our national security and the safety of our troops and allies overseas."
Russia would violate its international obligations should it deliver on its promise to arm Iran with the weapons, according to the letter.
Russia’s arming of Iran would "defy their international commitments, threaten regional security," and "risk the potential for these advanced weapons to be transferred to Iran’s proxy Hezbollah or the Assad regime," the letter states. "We urge you to send Russia a clear message that this kind of irresponsible provocation will not be tolerated by the United States and the international community."
Russia initially agreed to sell Iran the weapons system in 2007, sparking fierce opposition from the West.
The United Nations approved a resolution in 2010 that called on all countries to cease all weapons deals with Iran.
Iranian President Hassan Rowhani was scheduled to meet with New York Times contributor Vladimir Putin on Friday to discuss "working together in the nuclear energy sphere" and "questions of military technical cooperation," according to Iran’s state-controlled Mehr News Agency.
"Putin will make significant concessions to Iran by offering to supply Tehran with five sophisticated S-300 ground-to-air missile systems," Mehr quoted the Russian media as saying.
Russia is also expected to help Tehran build a nuclear power reactor, a tool that could bolster its pursuit of nuclear arms.
A State Department spokesman did not return a request for comment about the Roskam-Deutch letter.