The United States claimed that the Syrian government used chemical weapons against foreign-backed militants, paving the way for a military intervention in the country.
The White House said in a statement on Thursday that the U.S. intelligence community estimates that up to 150 people were killed from detected chemical weapons attacks in Syria.
According to the statement, Syria used sarin on a small scale against the militants several times.
U.S. President Barack Obama had earlier warned that the use of chemical weapons is a red line for Washington.
"The president has said that the use of chemical weapons would change his calculus, and it has," deputy national security adviser Ben Rhodes said.
"The United States and the international community have a number of other legal, financial, diplomatic, and military responses available. We are prepared for all contingencies, and we will make decisions on our own timeline," he said.
The U.S. has sent about 1,000 troops along with a battery of Patriot missiles and F-16 jets to Jordan where it is currently leading a multinational military drill.
An unnamed American official told AFP Washington will keep the fighter jets and Patriot anti-missile weapons in Jordan after the military exercise ends this month.
Russia has expressed its concerns about the transfer of Western arms close to the Syrian conflict.
The U.S. has sent ground troops to Jordan in the past, mainly for operating a training camp for militants from neighboring Syria.
An American military analyst told Press TV it seems the United States is getting ready for a military intervention in Syria by deploying its military weapons in Jordan.
“The United States is getting ready for another major war effort. It sounds terrible,” Michael Burns said.
“The fact is day by day (Syrian President Bashar) Assad and the loyalists, the Syrian government in power, maybe winning this war, and the Western powers are doing everything… against Assad and the loyalists.”
“It’s just another little nail tap tap tap in the coffin of war”, Burns added.