USA officials have in recent days said additional action would follow if Assad were to use the banned weapons in rebel-held Idlib.
Russian Federation and Iran insisted that a military offensive in Idlib would be a counter-terrorism operation and that measures would be taken to spare civilians.
He told council members there is "an urgent need" to separate opposition fighters seeking a political settlement from the "terrorists" in Idlib, and appealed to those with influence to exert pressure to achieve this.
Turkey, fearing an influx of refugees in the event of a major assault, has repeatedly warned against a "massacre" in this last stronghold of the Syrian opposition.
The second factor is the potential use of chemical weapons by Syrian government forces.
Last week, the United Nations warned that such an offensive would likely lead to the "worst humanitarian catastrophe of the 21st century".
Other aid organisations also operate in the area, but their support is mostly limited to providing supplies to civilians already living in the existing border camps.
Humanitarian crisis worsens in Syria as crippling assault on Idlib continues
Turkey is a leading opposition supporter which has troops in the country and has erected 12 observation posts around Idlib.
"In a complex place like Idlib, traditional counter-terrorism methods would not yield the desired results".
Complicating matters, the Turkish armed forces also have several outposts in Idlib in support of rebel groups.
"If Assad, Russia, and Iran continue down the path they are on, the consequences will be dire. The world will hold them responsible", she told the Security Council.
The German Defense Ministry is reportedly in talks with the US on potentially taking an active role in airstrikes in the event that Syria's President Bashar al Assad uses chemical weapons in Idlib province. "And no number of Security Council meetings will ever change that", said UN Representative Nikki Haley at a UNSC meeting on Tuesday.
"In this sense, a military operation in Idlib would only play into the hands of terrorists", he said.
"This is what we should be discussing today, Madam President, but I think it has been absent from the briefing we received from Russian Federation just now", Pierce added.
"Because today they are there, tomorrow they will be in some other countries, and in Europe also, or maybe in the United States".
On Tuesday, Russia claimed that Syrian rebels had begun working on film footage that would be presented to the world as the aftermath of an alleged chemical attack by the Syrian army.