"One thing needs to be clear: If someone shoots at our planes, we will destroy them".
The West blamed the chemical weapons attack on the Syrian government, days after which, in retaliation, the US, United Kingdom and France carried out joint missile strikes on Syrian military bases on April 14.
The Damascus sky lights up missile fire as the US launches an attack on Syria targeting different parts of the capital early Saturday, April 14, 2018.
Russian Federation had originally signed a contract in 2010 to supply Syria with four S-300 batteries, however after the outbreak of the Syrian civil war the following year and following pressure from Israel, Moscow cancelled the deal.
Russian President Putin described the missile attack on Syria on the night of April 14 as an act of aggression.
Israel has recently warned Iran against any moves to augment its military presence in Syria, where Iranian military advisers and militias have long provided critical support to Assad in his seven-year civil war against Sunni rebels.
Royce added that "at the same time as this carnage is going on, representatives of Syria, Iran and Russian Federation have spread out across the global community trying to gin up reconstruction money", but "they will not find it here".
Top Russian officials said earlier in April, that Moscow may reconsider a pledge it gave a decade ago not to provide Syria with the S-300 system in light of the air-strikes on Syria in April. Thousands of Douma residents left the town after the attack while Russian military police and Syrian security forced deployed in Douma, raising criticism from opposition activists the evidence may be tempered with.
Amid the escalating rhetoric, Russia's ambassador to Israel on Wednesday sought to downplay tensions between the two countries saying that Moscow's deployment of air defense systems in Syria was not related to Israel.
Russian Federation has arrayed S-300 and S-400 systems around its main bases in Syria near northeastern Latakia and has claimed that the U.S., France and Britain deliberately avoided the area for fear of interceptions during the April 13 missile strikes.
In February, Israel shot down what it said was an armed Iranian drone that penetrated its airspace from Syria.
The head of the International Committee of the Red Cross says the organization has been "flooded" with about 13,000 requests in the last six months from Syrians looking for missing family members.
Russian military sources told Kommersant that if Israel tried to destroy the anti-aircraft batteries, it would be "catastrophic for all sides".
"Unfortunately, as the U.S. Holocaust Memorial Museum noted in a recent report, the situation on the ground is getting even worse in Syria, and the worst is probably yet to come".