The White House has warned the Syrian regime it will pay a "heavy price" if it carries out another chemical attack on its citizens.
In a statement, President Donald Trump's administration said it had found evidence the Assad regime was preparing another attack on its own citizens.
The White House said it had observed activity similar to that seen before the chemical weapons attack the regime carried out on 4 April.
When Syrian leader Bashar al-Assad last launched a chemical weapons attack on his people, Trump responded by launching a missile against the country, the first major military action of his presidency.
White House press secretary Sean Spicer said in a statement: "The United States has identified potential preparations for another chemical weapons attack by the Assad regime that would likely result in the mass murder of civilians, including innocent children.
"As we have previously stated, the United States is in Syria to eliminate the Islamic State of Iraq and Syria. If, however, Mr Assad conducts another mass murder attack using chemical weapons, he and his military will pay a heavy price."