The demonstrations broke out early Saturday following a wave of U.S., British and French military strikes to punish President Bashar Assad for suspected chemical attack against civilians.
The targets included a scientific research facility near Damascus, a chemical weapons storage facility west of the city of Homs, and a third location near Homs that contained both a command post and a chemical weapons equipment storage facility, the United States military said.
Pentagon spokeswoman Dana White later told reporters that the US, Britain, and France "successfully hit every target", countering claims that some missiles were intercepted by Syrian air defenses. "We met our objectives".
No military measures were immediately announced, but in a clear warning to the US and its allies, Col. Gen. Sergei Rudskoi of the Russian military's General Staff said Moscow could boost Syria's Soviet-era air defence assets with batteries of state-of-the-art S-300 missiles.
The Pentagon reported Saturday a massive spike in online Russian propaganda efforts in the hours before and after the US missile strike on Syria the night before.
Trump announced from the White House on Friday night that the U.S., in coordination with France and the United Kingdom, had launched strikes on Syria following a week of threats of retaliation for an alleged chemical weapons attack on civilians by the Assad regime.
In that instance, 59 Tomahawk missiles were fired at a Syrian airbase in the western part of the country following a chemical attack blamed on Assad's forces.
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She added: "This action risks not just further escalating the civil war in Syria but also a unsafe escalation of global tensions". Often when the British government decides on military action, the opposition offers its full support .
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On Friday, Russian military chiefs claimed they had evidence the United Kingdom had directed the attack in Douma using the White Helmets, a group of humanitarian volunteers on the ground.
Russia's Defense Ministry said they did little damage. The Syrian government has denied the accusations. First, the USA strikes may not stop Assad from using chemical weapons, or turn the the tide of seven-year-long civil war. "We have sent a clear message to Assad and his murderous lieutenants".
Lt. Gen. Kenneth McKenzie, director of the Joint Staff, said that none of the aircraft or missiles involved in this operation were successfully engaged by Syrian air defenses, and there is no indication that Russian Federation air defense systems were employed.
The White House said doctors and aid organizations on the ground in Douma reported "the strong smell of chlorine and described symptoms consistent with exposure to sarin".
The Pentagon said America is ready if anyone should retaliate.
Defense Secretary Jim Mattis said no additional strikes were planned. Some of those more than 40 Syrian missile interceptors, he suggested, might have hit civilian targets. He said the targets selected by U.S., British and French officials were meant to minimize civilian casualties.
The U.S. military has about 2,000 troops in Syria, mostly in the northeast of the country where they are supporting a local alliance of militias battling the Islamic State.
"I'm not going to say that they're going to be unable to continue to conduct a chemical attack in the future".
Syrian surface to air missile batteries had attempted to fire back, but there were no initial reports of allied losses, he added.