In a warning to Russia, the Pentagon said Tuesday that the U.S. maintains the right to self-defense against advanced anti-aircraft systems sent to Syria by Moscow.
"This is something that we take very, very seriously -- the safety of our aircrews," Pentagon Press Secretary Peter Cook said in response to reports that Russia sent highly mobile S-300 anti-air missile systems (known to NATO as the SA-23) to its naval facility in the northwestern Syrian port of Tartus over the weekend.
"Those aircrews have the inherent right to self-defense," Cook said at a Pentagon news conference.
This marks the first time the system has been deployed outside Russian territory, according to the BBC. Last year, Russia deployed S-300s and the more advanced S-400 systems around its Khmeimim air base near the coastal city of Latakia, the hub of its air operations in support of the regime of Syrian President Bashar al-Assad.
Russia has no need of advanced surface-to-air systems in Syria given its stated aim of focusing operations on the Islamic State and Jabhat Fateh al-Sham, the al-Qaida affiliate formerly known as the Al-Nusra Front, Cook said.
"The last I checked, the Russians said their primary goal was to fight extremism. Neither one of them has an air force," Cook said of the two militant organizations.
"We're obviously tracking very closely" the placement of the Russian air defenses, he said.
Already frayed U.S.-Russia relations have deteriorated even further since the collapse of last month's "cessation of hostilities" in Syria and the fierce bombardment of Aleppo by Russian and Syrian air forces, with the intent of driving out rebels holding the eastern part of the city.
U.S. Secretary of State John Kerry on Monday announced that talks with the Russians on renewing the cease-fire had been suspended.
Cook said U.S. air operations against ISIS in northeastern Syria are continuing.
He also said that neither the White House nor the State Department has asked the Defense Department to plan for relief airdrops to Aleppo or to provide air cover for U.N. humanitarian convoys.
In a statement, Maj. Gen. Igor Konashenkov, a Russian Defense Ministry spokesman, confirmed that the S-300 system had been sent to Syria and questioned why the deployment raised U.S. concerns.
"The S-300 anti-aircraft missile system has indeed been sent to the Syrian Arab Republic," Konashenkov said. "I remind you that the S-300 is a purely defensive system and poses no threat to anyone. It's not clear why the placement of S-300 in Syria has caused such a stir among our western colleagues."
-- Richard Sisk can be reached at Richard.Sisk@Military.com.