Syrian President Bashar al-Assad may be preparing a chemical-weapons attack that would result in the "mass murder" of civilians, the White House has said while warning Syria's government that it would pay a "heavy price" if it goes ahead.
The White House on Monday said US intelligence observed potential preparations similar to those in the run-up to a deadly chemical attack on the opposition-held town of Khan Sheikhoun in April that the US blamed on Assad's forces.
More than 70 people were killed in that attack, including many children.
The US launched missile strikes against a Syrian air base in response.
READ MORE: Khan Sheikhoun attack survivors recall horror
"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," Sean Spicer, White House spokesperson, said in a statement.
"The activities are similar to preparations the regime made before its April 4, 2017 chemical weapons attack."
Assad has strongly denied the allegation that his forces used chemical weapons in Khan Sheikhoun, describing it as a "100 percent fabrication".
Conflicting claims
Assad has said repeatedly that his forces turned over all chemical weapons stockpiles in 2013, under a deal brokered by Russia to avoid threatened US military action.
The agreement was later enshrined in a UN Security Council resolution.
However, Jim Mattis, the US defence secretary, has previously said that there is "no doubt" that Syria has in fact retained some chemical weapons.
Syrian forces used nerve gas in four attacks: HRW
Human Rights Watch, the US rights organisation, said in May that Syrian forces used nerve gas in four attacks since December - part of a "clear pattern" that could amount to war crimes.
"As we have previously stated, the United States is in Syria to eliminate the Islamic State of Iraq and Syria," Spicer said in his statement, referring to the Islamic State of Iraq and the Levant (ISIL) group.
"If, however, Mr Assad conducts another mass murder attack using chemical weapons, he and his military will pay a heavy price."
The US-led coalition and allied fighters are battling to dislodge ISIL, also known as ISIS, from its Syrian stronghold of Raqqa.
The coalition is also backing a major assault on the last ISIL-held pockets of Mosul in neighbouring Iraq.
Russia is flying a bombing campaign in Syria in support of Assad, while the US is heading a coalition mainly targeting ISIL.
OPINION: Absurdity is questioning a dictator's motives
Neither the US, which backs the opposition, nor Russia, a longtime ally of the Syrian government, has managed to find a solution to the conflict.
Syria's war began in March 2011 with anti-government protests that escalated into a complex conflict that has killed more than 320,000 people and displaced millions.
Opposition groups are now on the back foot following Assad government's advances with support from Russia and Iran.
