The Eurocontrol airspace organisation said that the European Aviation Safety Agency (Easa) had sent a "Rapid Alert Notification" that flight operations needed to consider the possibility of air or missile strikes into Syria.
Trump's tweet was reacting to a warning from Russian Federation that any United States missiles fired at Syria over the deadly assault on Saturday on the rebel enclave of Douma near Damascus would be shot down and the launch sites targeted.
Senior Russian lawmaker, Alexei Kondratyev, a deputy head of the upper house's defense committee, on Wednesday said that warships would be engaged in the Mediterranean Sea to protect Russian assets in Syria from a possible United States strike.
"I think it's very unlikely that we would directly and intentionally target any Russian forces that are in Syria, so the way that a Russian officer or person would be harmed is by participating directly in Syrian military activity".
The ruble sank to a 16-month low in intraday trading on Wednesday after U.S. President Donald Trump warned Russian Federation on Twitter to get ready for missile strikes in Syria.
Both Damascus and Moscow have vehemently denied involvement in the alleged chemical attack and accused rebel groups of fabricating the attack to hinder the army's advances and provoke worldwide military intervention.
"We have proof that last week chemical weapons were used, at least chlorine, and that they were used" by Assad's forces", he also said.
Defense Secretary Jim Mattis on April 12 said he personally believed an "inexcusable" use of chemical weapons had taken place in Syria.
Asked in a TV interview whether France would join strikes on Syria, he said, "We will need to take decisions in due course, when we judge it to be most useful and effective", according to Agence France Presse. We can not risk an escalation even further than it's gone'.
United States President Donald Trump on Thursday appreciated the USA state administration for handling the militant group Islamic State in Syria.
President Donald Trump is said to be preparing to tip off the Russian military before launching any missile strike on Syria, so that Moscow can get its forces out of the way.
"We should all be outraged at these horrific reports and images from Douma" where Saturday's attack took place, said Peter Salama, the United Nations agency's chief of emergency response. "Could be very soon or not so soon at all!" said Trump in his latest early morning tweet.
"I am not going to comment on USA military actions".
The response by the Syrian government is that the incident had been staged as provocation by the terrorist group Jaish al-Islam and other militants to prevent the advance of the Syrian government's army.
Ali Akbar Velayati, a top adviser to Iran's Supreme Leader Ali Khamenei, said the Western threats were "based on lies" about the poison gas assault, after meeting Assad.
His comments raised the prospect of direct conflict over Syria for the first time between the two world powers backing opposing sides in the seven-year-old civil war, which has aggravated instability across the Middle East.
Tass, in a news story out of the northern Syria city of Homs, quoted Russian lawmaker Dmitry Sablin as rejecting reports that Assad may have fled Syria.
Assad, along with his Russian backers, warned again on Thursday that the threat of military action from the US, "and any possible actions, will only contribute to further destabilization in the region".
At the eye of the storm, Assad said any Western action "will contribute nothing but an increase in instability in the region, threatening worldwide peace and security", Syrian state television reported.