Should the President follow through on his warnings of an attack, two US Navy destroyers armed with Tomahawk cruise missiles are in position and ready to be called into action, among other assets, including jets and submarines.
The Syrian Army reports shooting down 20 US, UK and French missiles.
The US military struck targets that were "specifically associated" with Syria's chemical weapons program while minimizing the risk to civilians, according to chairman of the Joint Chiefs of Staff Joseph Dunford.
The Organization for the Prohibition of Chemical Weapons, based in the Netherlands, announced it was sending a fact-finding team to the site of the attack outside Damascus, and it was due to arrive Saturday.
The decision by the U.S. to strike marked Mr Trump's second order to attack Syria; he authorised a barrage of Tomahawk cruise missiles to hit a single Syrian airfield in April 2017 in retaliation for Syria's use of sarin gas against civilians.
Meanwhile, in Britain, the cabinet agreed in principle "on the need to take action" in Syria to "deter the further use of chemical weapons", a Downing Street statement stated. "Russia was supposed to guarantee Assad would not use chemical weapons, and Russian Federation did the opposite". British officials said up to 75 people were killed.
In 2013, President Putin and his government promised the world that they would guarantee the elimination of Syria's chemical weapons.
Earlier Thursday, Trump appeared to walk back comments in which he warned Russian Federation to brace for missiles, which he said "would be coming". He also said there were "no reports of losses" on the part of the US and its allies. The Kremlin said a crisis communications link with the United States, created to avoid an accidental clash over Syria, was in use. "Every American, and particularly our men and women in uniform and their families, deserve far better than action without debate, accountability, and a Constitutionally-required authorization for the use of military force", he said in a statement.
"We are prepared to sustain this response until the Syrian regime stops its use of prohibited chemical agents", Trump said.
"I do think there's the possibility of a military confrontation between the United States and Russian Federation in Syria", Morrell said.
The US military, assisted by forces from the United Kingdom and France, launched the strikes targeting chemical weapons operations this morning Australian time to punish President Bashar al-Assad for his alleged use of chemical weapons against his people. Trump said Thursday on Twitter. "These are not actions of a man, they are crimes of a monster instead". He also suggested he was examining ways to prevent any strikes from triggering a broader conflict.
Trump also had strong words for Syria's allies. He said the three nations have "marshaled their righteous power".
And he described the Middle East as a "troubled place".
The U.S. stance on striking Syria is no clearer, even after President Trump tweeted that missiles "will be coming".
Activists and rebels in Syria claimed that Syrian forces used chlorine gas in the attack on April 7 against Douma in the rebel-held area near Damascus.
The U.S. has about 2,000 troops on the ground in Syria as advisers to a makeshift group of anti-Islamic State fighters known as the Syrian Democratic Forces.
The Organisation for the Prohibition of Chemical Weapons, the global watchdog, confirmed a fact-finding team was on its way to Syria and would begin work on Saturday. Gen. Igor Konashenkov, speaks at a briefing in Moscow on Friday, April 13, 2018.
US President Donald Trump said yesterday he was holding meetings to discuss the crisis in Syria and that a decision would be taken "fairly soon" on threatened missile strikes in response to the suspected poison gas attack on a rebel stronghold.
Mr May and Mr Trump are believed to be in agreement that the Syrian regime, lead by President Bashar al-Assad, must not go unchallenged.
The White House said it was still assessing the evidence after its security council meeting on Thursday.
He told Sky News: "If there is proof the regime did it, then the regime must be held responsible".
While the prospect of US-led military action that could lead to confrontation with Russian Federation hung over the Middle East, the White House on Friday accused Syria of carrying out a toxic gas assault on April 7 that killed dozens of people in Douma, near Damascus.
Vassily Nebenzia, Moscow's ambassador to the United Nations, said he "cannot exclude" war between the United States and Russian Federation and urged Washington and its allies to refrain from military action against Syria.
The minister said strikes conducted by French air force in Syria not targeted at Syria's allies.