The jihadist group is fighting to overthrow President Bashar al-Assad's regime and establish a caliphate.
Russia has made threats to strike down any missiles using its powerful S-400 defence system if any were to be launched at Assad's forces.
"Due to the possible launch of air strikes into Syria with air-to-ground and/or cruise missiles within the next 72 hours, and the possibility of intermittent disruption of radio navigation equipment, due consideration needs to be taken when planning flight operations in the Eastern Mediterranean/Nicosia FIR area", it said, referring to the designated airspace, Reuters reports.
Speaking on TF1 television, Macron said that France would not tolerate "regimes that think everything is permitted".
At least 500 others were treated for symptoms "consistent with exposure to toxic chemicals", the World Health Organization said Wednesday.
At stake in Syria is the potential for confrontation, if not outright conflict, between the US and Russia, former Cold War foes whose relations have deteriorated in recent years over Moscow's intervention in Ukraine, its interference in the 2016 US presidential election and its support for Syrian President Bashar Assad.
In a follow-up tweet, Trump said America's relationship with Russia "is worse now than it has ever been". "Our intelligence tells us otherwise".
"First of all, we are committed to ending that war through the Geneva process and the UN-orchestrated effort". "If you do, you make a mistake".
"We are studying that situation extremely closely".
The US State Department said the United States has proof at "a very high level of confidence" that the Syrian government carried out the attack but is still working to identify the mix of chemicals used.
Mr Corbyn said there must be an inquiry to find out who was responsible. "There is no reason for this".
Russian jamming equipment has been documented on the frontline on numerous occasions, and other elements of their electronic warfare capabilities have also been recorded.
Meanwhile, U.S. officials say blood and urine samples from victims of the attack have tested positive for traces of chemical gas.
"The immediate priority", he said, "is to avert the danger of war". Britain charged again that it was Russia, but Moscow insisted the findings mean nothing.
Ministers also agreed that Mrs May should continue to work with the United States and France to come up with the right response.
But with less than a year to go until Britain leaves the European Union, Mrs May wants to deepen its "special relationship" with the United States with a wide-ranging free trade deal that would help cushion the impact of Brexit.