The White House on Monday cautioned the Syrian government against using chemical weapons, warning President Bashar al-Assad that there would be a "heavy price" if his regime used the weapons again.
The last known use was on April 4, when a chemical weapons attack killed scores of civilians, including children. President Donald Trump responded by launching cruise missiles at an airbase in Syria believed to be the source of the weapons.
The White House issued a statement threatening the Syrian regime, saying the United States would punish Assad if he used chemical weapons on the Syrian people.
"As we have previously stated, the United States is in Syria to eliminate the Islamic State of Iraq and Syria," the statement said. "If, however, Mr. Assad conducts another mass murder attack using chemical weapons, he and his military will pay a heavy price."
Russia responded angrily to the White House's statement, calling it an "unprecedented provocation." A spokesman for the Kremlin called the threat to the Assad regime "unacceptable."