The Pentagon said: "The Department of Defense is not conducting air strikes in Syria".
The preparations follow a pattern of evacuations around the capital, Damascus, and other major Syrian cities as the government reasserts its control after seven years of war.
Syria initially said the West was involved.
'President Putin, Russia and Iran are responsible for backing Animal Assad.
"We are on the edge of a unsafe precipice", she said.
Explosions have been heard around the T-4 airbase located in the suburbs of Homs in Syria, state-run Syrian Arab News Agency reported, citing an unidentified military source.
Then, within days the USA military fired cruise missiles at a Syrian airfield where the sarin attack had been launched from.
The ministry says Syria shot down five out of the eight missiles that targeted the base.
Bakkar, the opposition activist, said several bombs laced with chemicals landed in Douma Saturday night.
The Israeli government had no immediate comment.
Russian Ambassador Vassily Nebenzia said Moscow had told the United States that it would not allow its forces on the ground in Syria to be put at risk.
US officials told Reuters that Washington was weighing a multinational military response.
Housing Minister Yoav Galant, while also not confirming that Israel had carried out the attack, said: "We have clear interests in Syria".
However Trump laid the blame firmly at the feet of Syrian President Bashar Al-Assad and his chief backers, echoing similar statements from the European Union and Turkey. "Probably after the fact", Trump said.
In response to the reports, Trump on Sunday blamed Syrian government forces for what he called a "mindless CHEMICAL attack".
The Observatory gave a higher death toll, saying at least 80 people were killed in Douma, including around 40 who died from suffocation.
"The numbers keep rising as relief workers struggle to gain access to the subterranean areas where gas has entered and hundreds of families had sought refuge", the group said.
Those reports could not be independently verified because of a government blockade around the town.
During a bitter clash at the Council, US Permanent Representative Nikki Haley said that the hands of the Russian "regime" were "covered in the blood of Syrian children" and warned that Washington would respond to the attacks even if the Council would not.
But a United Nations war-crimes investigation found the Assad regime was responsible for the attack past year in Khan Sheikhoun.
"The Secretary-General is particularly alarmed by allegations that chemical weapons have been used against civilian populations in Douma", a spokesman for U.N. Secretary-General Antonio Guterres said in a statement.
Russian Federation and Syria both offered during the U.N. Security Council meeting on Monday to take OPCW investigators to Douma.
On Sunday, Trump tweeted in response to the reports of the alleged chemical attack on Douma, saying Russian Federation and Iran were responsible for backing "Animal Assad" and warning there would be a "big price to pay".
UOSSM said doctors could not determine the origin of the chemical attacks.