A tractor clears rubble on August 13, 2018 following an explosion at an arms depot in a residential area in Syria's northern Idlib province city of Sarmada. | Aaref Watad/AFP/Getty Images White House 'monitoring' possible Syrian offensive that defies Trump warning

The White House on Tuesday said it is "closely monitoring" an imminent major Syrian regime attack on rebel holdouts in Syria's Idlib province—a military action that would defy admonitions from President Donald Trump and other senior U.S. officials.

"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," press secretary Sarah Huckabee Sanders said in the statement, which specifically cited the roles of Russia and Iran in what could be the last major offensive of Syria’s long and bloody civil war.


Russian and Syrian jets have begun bombing the province, according to Reuters, killing 13 civilians but no Syrian rebel fighters. Moscow and Tehran have backed Syrian president Bashar al-Assad’s long campaign to snuff an insurgency that plunged his country into civil war in early 2011.

Sanders said the U.S. "will continue to work tirelessly with its Allies to find a lasting diplomatic solution to resolve the hostilities in Syria." But despite the U.S.’s repeated efforts to make Moscow rein in both Assad and his Iranian partners, Russian President Vladimir Putin has been largely unmoved.

Trump on Monday warned Syria, Russia and Iran to not attack that area, noting a widely-cited risk of massive civilian casualties in Idlib, where anti-Asad rebels have consolidated and dug in for what many experts believe could be their last stand against an overwhelming military offensive.

"President Bashar al-Assad of Syria must not recklessly attack Idlib Province," Trump wrote on Twitter. "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!"

Sanders also said in a statement that the U.S. and its allies "will respond swiftly and appropriately" if Syria uses chemical weapons again. Trump has twice ordered air strikes on Syrian regime forces and facilities as punishment for past chemical weapons attacks on civilian areas.

"Let us be clear, 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," Sanders continued in a statement.

The statement comes amid a new claim that Trump called for Assad’s assassination after a 2017 chemical weapons attack.

“Let’s fucking kill him! Let’s go in. Let’s kill the fucking lot of them,” Trump said to Defense Secretary Jim Mattis, according to excerpts from a book by Bob Woodward, entitled "Fear: Trump in the White House," and published Monday by the Washington Post.

Woodward writes that Mattis told Trump he would do so, but after getting off the phone told a senior aide: “We’re not going to do any of that. We’re going to be much more measured.”

Trump has frequently said that he believes the U.S. should play little or no role in Syria, with Arab allies like Saudi Arabia shouldering more of the burden of stabilizing and reconstructing the war-torn country. But he has also complained sharply about Iranian influence in the country and angrily accused Russia of enabling Assad's chemical weapons attacks.

Many senior U.S. diplomatic and military officials believe it is important for the U.S. to maintain a military presence in the country, where American troops have been fighting the Islamic State in Syria's eastern region—both to ensure the terrorist group does not make a comeback, and to check Iranian military influence that Israel also vehemently opposes.