"The Russian delivery of further enhanced air defenses to the Assad regime will only raise the risk of escalation in an already dangerous environment and increase the risk to US and partnered forces conducting D-ISIS operations in Syria," the State Department official said in an interview for Sputnik.
"It also reconfirms Russia's continued protection of the Assad regime and ultimate responsibility for the regime's actions," the official added.
The State Department official recalled that the Syrian anti-aircraft systems shot down Russia’s aircraft.
"Introducing even more air defenses does not solve the problem of Syria’s unprofessional and indiscriminate firing of missiles, or reduce the risk to regional aviation," the State Department official said.
In addition, the official characterized said the death of the Russian aircrew as "an unfortunate incident."
"It reminds us that the many overlapping conflicts in the region need permanent, peaceful, and political resolutions in accordance with UN Security Council Resolution 2254," the official said.
The incident underlines "the danger of escalation in Syria’s crowded theater of operations," and that "Iran must end its provocative transit of dangerous weapon systems through Syria that are a threat to the region," the official added.
Earlier on Monday, Russian Defense Minister Sergei Shoigu announced measures on increasing security of Russian servicemen in response to the crash of Russian Il-20 military aircraft, which Russia believes Israel is responsible for. Shoigu explained Russia would equip the Syrian air defense forces’ command posts with automatic control systems, which had been previously possessed only by Russia, jam satellite navigation, on-board radars and communication systems of combat aviation attacking Syrian targets and, most importantly, supply S-300 air defense systems to Syria.