File Photo: A Syrian soldier looks on as Syrian forces enter the Kharab al-Shahem town in the western countryside of Daraa province in southern Syria on July 8, 2018. (Xinhua/Ammar Safarjalani)

WASHINGTON, Sept. 4 (Xinhua) -- The White House said on Tuesday that it would "respond swiftly and appropriately" if Syria uses chemical weapons in Idlib province.

In a statement, the White House said, "It remains our firm stance that if President Bashar al-Assad chooses to again use chemical weapons, the United States and its Allies will respond swiftly and appropriately."

"The United States is closely monitoring the situation in Idlib province, Syria, where millions of innocent civilians are under threat of an imminent Assad regime attack," it said, accusing the alleged possible attack of being "backed" by Russia and Iran.

"President Donald J. Trump has warned that such an attack would be a reckless escalation of an already tragic conflict and would risk the lives of hundreds of thousands of people," said the White House.

"The United States will continue to work tirelessly with its Allies to find a lasting diplomatic solution to resolve the hostilities in Syria under the auspices of United Nations Security Council Resolution 2254," it said.

Since earlier this year, the Syrian rebels were driven out of key areas in the capital Damascus, the central province of Homs and the southern region.

The government's army has been amassing forces and military gears around Idlib in recent weeks, as the last major battle against the rebels in Syria looms.

Trump tweeted Monday that Syrian President Bashar al-Assad "must not recklessly attack Idlib Province."

"The Russians and Iranians would be making a grave humanitarian mistake to take part in this potential human tragedy. Hundreds of thousands of people could be killed. Don't let that happen!" He said.

The Kremlin responded later that Trump's warning to Syria not to attack the rebel-held Syrian province ignored the danger terrorists pose there.

Kremlin spokesperson Dmitry Peskov said that Idlib will be one of the main issues on the agenda of the Russia-Turkey-Iran summit to be held in Tehran on Friday.

Idlib, with a population of about 2.5 million, is strategically important as it shares a border with Turkey to the north, and also hosts a Russian-operated air base. It is close to the coastal province of Latakia, home of Syrian President Bashar al-Assad.