The White House says it has found "potential" evidence Syria is preparing for another chemical weapons attack.
Press secretary Sean Spicer issued an ominous statement on Monday that the US, "has identified potential preparations" for another chemical attack by the Syrian Government that it says, "would likely result in the mass murder of civilians, including innocent children".
He says the activities are similar to those made before an April chemical attack.
The Trump administration launched missile strikes in retaliation for that attack, which it blamed on Syrian President Bashar al-Assad.
Mr Spicer warned, "if Assad conducts another mass murder attack using chemical weapons, he and his military will pay a heavy price".
The White House provided no immediate evidence to back up its claims.
The United States has taken a series of actions over the past three months demonstrating its willingness to carry out strikes, mostly in self-defence, against Syrian government forces and their backers, including Iran.
The US ambassador to the United Nations Nikki Haley said on Twitter: "Any further attacks done to the people of Syria will be blamed on Assad, but also on Russia and Iran who support him killing his own people."
Since the April military strike, Washington has repeatedly struck Iranian-backed militia and even shot down a drone threatening US-led coalition forces.
The US military also shot down a Syrian jet earlier this month.
Mr Trump has also ordered stepped-up military operations against the Islamic State militant group and delegated more authority to his generals.
AP/Reuters
