Trump posted in Twitter.
He added: "Through the relevant channels we already conveyed to the United States that armed force under mendacious pretext against Syria - where, at the request of the legitimate government of a country, Russian troops have been deployed - could lead to grave repercussions". Trump also pointed out that Mueller's team is staffed entirely with Democrats and people who worked for President Barack Obama.
Anticipating a retaliatory attack from the US, and after Russia jammed some less significant USA drones following suspected chemical weapons attacks on civilians in eastern Ghouta several weeks ago, Russians started jamming major US drones in Syria, according to the four officials.
The Russian military said it had observed the movement of USA naval forces in the Gulf. In its calculations, the USA military has factored in the probable loss of a handful of Tomahawk missiles, the likely main weapon of choice, to anti-missile systems, none of which will significantly undermine the impact of a strike. The three countries are discussing a range of options, including preventing Assad from conducting future attacks by striking military capabilities involved in carrying out such attack, the official said.
She said: "It is truly horrific to think of victims, families sheltering underground when the chlorine found them". The military expenditure of the United States is up to $700bn. It was unclear whether his remarks reflected any unease about Trump's apparent move toward military action.
This latest warning from Russian Federation came during UN Security Council meeting where an inquiry into the chemical attack failed to pass.
Moscow's threat to down United States missiles came from its ambassador to Lebanon, Alexander Zasypkin, who said it was based on previous statements by President Vladimir Putin and the Russian armed forces chief of staff.
Russian Federation is Assad's most powerful ally and its devastating air power has helped him wrest back large areas of territory from rebels since 2015. During one speech, he said, "We must as a nation be more unpredictable".
Putin spoke to Israeli Prime Minister Benjamin Netanyahu on Wednesday and urged him to do nothing to destabilize Syria.
It is to be noted that a year ago when Syrian nerve agent attack happened which took lives of more than 80 people, Trump ordered the firing of dozens of cruise missiles at a Syrian government airbase.
With tensions growing, however, European air traffic control agency Eurocontrol warned airlines to exercise caution in the eastern Mediterranean due to the possible launch of air strikes into Syria over the next 72 hours.
Theresa May held separate calls with the two leaders on Tuesday.
Video: What will the USA do in Syria?
Syria's Russian-supplied air defences shot down an Israeli F-16 jet in February during a bombing run against what Israel described as Iranian-backed positions in Syria.