"Get ready Russian Federation, because they will be coming, nice and new and 'smart!'" He adds: "You shouldn't be partners with a Gas Killing Animal who kills his people and enjoys it!"
Trump, however, has not used similarly strong language about Russia's election activities which started as early as 2014.
When the US fired Tomahawk missiles at a Syrian airfield a year ago after a chemical weapons attack, the Pentagon gave Moscow advance warning to get its personnel out of harm's way.
He described the situation in Syria as "rather tense" but declined to specify how Moscow would respond to a US airstrike against its ally Assad.
"The president holds Syria and Russian Federation responsible for this chemical weapons attack", she said.
The Syrian pound lost almost 10 percent of its value on prospects of an American attack, going from about 430 Syrian pounds to the dollar last week to 469 Wednesday.
With the Middle East on edge and many fearing inadvertent triggering of a regional war, it's easy to forget that not so long ago President Donald Trump shocked advisers by declaring his intention to withdraw USA troops from Syria and "let others take care of it now".
Russian Foreign Ministry spokesperson Maria Zakharova posted on Facebook that "Smart missiles should fly toward terrorists, not the legitimate government that has been fighting global terrorism for several years on its territory".
"Everybody's drawing red lines and as soon as one side crosses the red lines, that forces the other side to respond", he said. There is no reason for this, he wrote, adding that "Russia needs us to help with their economy, something that would be very easy to do, and we need all nations to work together".
The tweet followed Russia's warning that it will strike at incoming US missiles and their launch platforms. "Stop the arms race?"
Trump and other Western leaders have vowed a quick and forceful response to Saturday's alleged gas attack, which rescue workers say killed more than 40 people in the Damascus suburb of Douma.
Asked about Trump's tweet about an impending attack on Syria, former Defense Secretary William Cohen, who ran the Pentagon for President Bill Clinton, said on CNN that it "compromises the mission somewhat".
French President Emmanuel Macron said his nation, the US and Britain will decide how to respond. McDonald has written the prime minister urging "extreme caution on the United Kingdom government's part in considering its response" and saying the party was not convinced a further escalation was the proper way forward.
Trump has been weighing his course of action in Syria following the suspected chemical attack, which he described as "sick" over the weekend.
Retired Lt. Gen. Yevgeny Buzhinsky, the former chief of the Russian Defense Ministry's worldwide department, warned that Russia has thousands of military advisers in Syria "practically in every battalion", and a strike on any Syrian facility could jeopardize their lives. This is not the first such attack on civilians during the civil war.
But many of Syria's most sensitive military facilities are protected by Russian missile defense systems or are located at bases where Russian, Iranian and Syrian personnel cohabit.
But asked if they would support military action if it results in conflict with Russian Federation, opposition rises to 48% and support falls to 28%, with 10% answering neither, 13% don't know.