As Syrians endured a new round of devastating violence over the past week, Ambassador Frederic Hof, the former envoy to Syria, says Syrian President Bashar Assad's government is now "testing President Trump's red line when it comes to using chemical warfare."

"I'm afraid that Assad is testing this president's chemical red-line. He's weaponizing the use of chlorine which, although is not deadly, it is nevertheless a very, very powerful instrument of terror," said Hof on CBS News' "Face the Nation" on Sunday.

Hof called Assad "the master of cynicism."

"He carefully takes the measure of everyone who comes up against him. He concluded, with respect to President Obama, 'If I don't use sarin gas, I can use anything I want,'" Hof added.

The Trump White House has condemned Assad's use of chemical weapons as constituting "war crimes" but has yet to offer a concrete solution. Mr. Trump has called the violence a "disgrace" but emphasized the U.S' role is purely to "get rid of ISIS and go home."

"Nearly a year ago, in April 2017, the United States intervened very forcefully, striking a Syrian air base in the wake of a sarin nerve agent attack by the Assad regime on civilians in northern Syria," Hof said, referring to the launch of nearly 60 cruise missiles against Syrian targets last year. "I suspect there are people in Eastern Ghouta right now who are saying, 'Please, Mr. Assad, attack us with sarin because if you do perhaps the world will come to our assistance."

The latest attacks were carried out on civilians in several parts of Syria, particularly in the Idlib governorate and the rebel-held Damascus suburbs of eastern Ghouta.

In response, the U.N. Security Council unanimously voted to approve a resolution calling for a 30-day ceasefire across the country to deliver aid and evacuate the wounded.

But the former ambassador says a ceasefire has little chance of taking hold.

"Unfortunately, Margaret, there is a long list of U.N. Security Council resolutions instructing Syria to stop this kind of activity to permit the delivery of humanitarian assistance, both food and medicine," Hof said. "They've been ignored. It's good that this resolution was passed. It's good that it was passed unanimously but the early returns are not good. Bombing is reportedly ongoing as we speak."

Hof added that the question remains as to who is going to do the "heavy and sustained lift" needed to stabilize the region.

"The heavy lift that's going to be required to protect Syrian civilians because the lack of protection is a humanitarian and a geopolitical catastrophe," he said.