The Trump administration declaration came after the Kremlin criticized Trump's warnings against the expected offensive in the northern province, where Syria's rebels are holed up and have come under intense airstrikes.
Syrian rebel fighters from the recently formed "National Liberation Front" reinforce a position along the front near the village of Abu Dali in the Idlib province countryside on September 1, 2018, in anticipation of an upcoming government forces offensive.
His comments came as Syrian troops gathered near the north-western region of Idlib for a major assault that has raised fears of a humanitarian catastrophe on a scale not yet seen in the seven-year-old conflict.
Meanwhile, the Syrian Observatory for Human Rights said Russian air strikes battered Idlib on Tuesday for the first time in three weeks. More than 350,000 people have been killed and millions displaced since Syria's war started in 2011 with the brutal repression of anti-government protests.
Speaking in a meeting with visiting US Republican Senator Richard Hayden Black in Damascus on Wednesday, Assad said that Washington has long resorted to threats, punitive measures as well as state terrorism, stressing that it will be of great benefit to American statesmen and nation if Washington opts to secure peace than to foment strife and destabilize world countries.
President Bashar al-Assad's regime has retaken large swathes of the country from rebels and militants since Russian Federation intervened militarily on its side in 2015.
On Wednesday, Putin's spokesman Dmitry Peskov said Idlib was the "subject of increased concern and worry" and the focus of a flurry of diplomacy.
"If they want to continue to go the route of taking over Syria, they can do that, but they cannot do it with chemical weapons", she said.
Erdogan as well as the presidents of Iran and Russian Federation will meet on Friday in Tehran for a summit expected to focus on Idlib.
"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".
In April, Western countries accused Syria of being behind an alleged chemical weapons attack in the town of Douma.