Syrian President Bashar al-Assad has approved a gas attack in the Idlib province, which is the country’s last rebel stronghold, the Wall Street Journal reported on Sunday. Reports of Assad’s approval of a chlorine gas attack on Idlib comes almost a week after President Trump warned the Assad and his allies not to “recklessly attack” the province.  President Trump called any gas attack a potential “grave humanitarian mistake.”

U.N. officials believe an offensive on Idlib would trigger a wave of displacement that could uproot an estimated 800,000 people and discourage refugees from returning home. The U.S. and France have warned an Idlib offensive would trigger a humanitarian crisis and warned that a chemical attack in Idlib would prompt a western retaliation.

If Assad deploys the chemical against the approximately 70,000 remaining opposition fighters in Idlib, President Trump has privately threatened to deploy a massive attack against his regime, people familiar with the exchange told the Journal.

The Wall Street Journal reported that the international pressure from the U.N. and the U.S. did very little to sway Assad, who benefits from unwavering support from both Russia and Iran.

The White House, so far, has been  in their planning of a response to the reports.

“We haven’t said that the U.S. would use the military in response to an offensive,” one senior administration official told the Wall Street Journal. “We have political tools at our disposal, we have economic tools at our disposal. There are a number of different ways we could respond if Assad were to take that reckless, dangerous step.”