Defense Secretary Jim Mattis warned Syria on Sunday that it would be “very unwise” for the regime to use chemical weapons against civilians in the war-torn country, but stopped short of threatening to retaliate.

“Right now we’re getting reports — I don’t have evidence that I can show you — but I’m aware of the reports of chlorine gas use,” Mattis said as he headed to Oman, referring to reports that President Bashar al-Assad’s forces were bombing civilians.

Trump launched a cruise missile strike at a Syrian airbase last April after Assad used chemical weapons to attack civilians, killing more than 80 people, including many children.

Asked if the Trump administration was intending to react militarily, Mattis said the president has “full political maneuver room” to decide on a response.

“I’m not going to strictly define it. We have made it very clear that it would be very unwise to use gas” as a weapon, he added.

Mattis also condemned the killings of civilians in Assad’s offensive against rebels in Ghouta, a suburb of Damascus, and said Russia could be complicit in the slaughter.

The United Nations estimates that 400,000 civilians are caught in the fighting.

Mattis said reports show that Syrian troops are “at best indiscriminately” attacking civilians and “at worst targeting hospitals. I don’t know which it is, whether they’re incompetent or whether they’re committing illegal acts or both.”

But he said Russia, which has been propping up the Assad regime during the eight-year civil war, bears some of the blame.

“Either Russia is incompetent or in cahoots with Assad,” Mattis said. “There’s an awful lot of reports about chlorine gas use or about symptoms that could be resulting from chlorine gas.”

With Post Wires