Syrian President Bashar Assad denied that his regime carried out a chemical attack. | Joseph Eid/Getty Images White House threatens Syria over possible chemical attack

The White House, in a rare high-stakes gambit that took some national security veterans off guard, announced Monday it has evidence that Syria is preparing to launch another chemical attack and warned that it will “pay a heavy price” for doing so.

“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,” Press Secretary Sean Spicer said in a brief statement issued late in the evening. “The activities are similar to preparations the regime made before its April 4, 2017 chemical weapons attack.”


If Syrian President Bashar Assad “conducts another mass murder attack using chemical weapons,” the statement added, “he and his military will pay a heavy price.”

The public warning was seen as highly unusual -- reflecting both confidence in the intelligence information suggesting that another attack might be imminent and a willingness to take military action should the warning not be heeded.

A senior administration official said that President Donald Trump and his national security adviser, Lt. Gen. H.R. McMaster, were involved in the decision to issue a public warning.

The official said it was intended to send a strong message that Trump is prepared to take action again like he did after the April attack, ordering a salvo of Tomahawk missiles from U.S. warships at a Syrian airfield from where the chemical attack was launched. In other words, U.S. retaliation was not a one-off event.

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The April 4 chemical attack by Assad’s regime, launched from a Syrian warplane, left more than 80 people dead, including children young enough to still be wearing diapers when they were killed. Assad denied that his regime carried out the attack.

It also appeared to be a warning to Assad’s biggest backers, Russia and Iran. Trump’s ambassador to the United nations, Nikki Haley, weighed in afterward on Twitter: “Any further attacks done to the people of Syria will be blamed on Assad, but also Russia & Iran who support him killing his own people.”

It is not extraordinary for the U.S. to warn foreign governments against taking imminent actions that might provoke a severe American response. A former senior Obama administration official said that on at least one occasion, the U.S. became aware that Syria was preparing to use chemical weapons and delivered a private warning to the Assad regime through an intermediary.

But the public nature of Monday night’s warning shot surprised former officials.

“It is unusual we would warn them -- even more unusual in a White House statement,” said Jon Wolfsthal, who served as the senior director for arms control and nonproliferation at the National Security Council until January. “It has serious consequences. We are saying 'we are watching you, we can see you, don’t do it.' The United States would have to respond. Otherwise it raises serious credibility problems.”

He said it also raises the question of how confident U.S. intelligence agencies are about Assad’s activities. “What if we are mistaken? For the White House to issue a statement like this is pretty high stakes.”

Others expressed some concern that the Trump administration could come to regret the move.

“This is the decisive moment for the Trump Administration if Syria launches an attack,” said Jim Jeffrey, former U.S. ambassador to Turkey and Iraq and the former deputy national security adviser for President George W. Bush. “Clearly the administration’s last retaliatory strike, if this report is correct, did not deter Syria.”

“If Syria goes forward,” Jeffrey added, “the administration cannot launch another pinprick attack at obsolescent Syrian aircraft. The warning from White House talks of the “heavy price” not only Syrian regime but Assad must pay... That means striking top level Syrian leadership including Assad. Anything less will be seen as America blinking. We tried diplomacy, then limited retaliation, now it is all out or virtual capitulation.”

Even the threat of military action is sure to further strain an increasingly tense relationship between Washington and Moscow.

In remarks earlier this month, Russian President Vladimir Putin reiterated his insistence that Assad had not used chemical weapons against his people and called Trump’s April missile strike on a Syrian air file “a provocation” against Moscow’s closest Middle East ally.

“We are absolutely convinced that it was a provocation. Assad didn’t use the weapons,” Putin said at the time. “It was done by people who wanted to blame him for that.”

But the Trump administration has been consistent that it would not tolerate such attacks -- a departure from President Obama, who warned Assad in 2013 not to cross a “red line” by using weapons of mass destruction but did not follow through after evidence Assad’s forces used poison gas on a number of occasions against civilians.

Defense Secretary Jim Mattis told reporters at the Pentagon after the U.S. missile strikes in April that “if they use chemical weapons [again], they are going to pay a very, very stiff price.”

A White House official said Monday’s unusual public warning was designed to make that crystal clear.

“The strategy is, people shouldn’t tempt this president.”

Andrew Tabler, an expert on Syria at the Washington Institute for Near East Policy and an authority on Assad, said that’s a risky play.

“The alleged preparations [for a chemical attack] are the latest in a series of episodes over the past two months where Assad is escalating with the US, not the other way around,” Tabler said. “Will Russia and Iran support Assad as they have recently in southern and eastern Syria?”

Michael Crowley, Tara Palmeri, Nahal Toosi, and Rebecca Morin contributed reporting.