President Trump sent out a tweet on Tuesday, warning President Bashar al-Assad of Syria that he should not attack Idlib province. His tweet was also directed towards Syrian’s allies, Iran and Russia, who planned to assist in the offensive.

According to Bloomberg News, Syrian forces are planning an attack on the remaining rebel stronghold settled in Idlib territory. Trump claimed, in his tweet, that an attack on Idlib province would constitute as a “grave humanitarian mistake” and that “hundreds of thousands of people could be killed.”

If Assad’s forces were to attack as planned, the combat would be the last major battle of Syria’s civil war, given the territory is the last major area currently under control of rebel forces.

France shares President Trump’s thoughts, and has also advised against an offensive targeting on the rebel-controlled region of Idlib. The French Prime Minister, Jean-Yves Le Drian, informed authorities that 2 million people reportedly live in the region and would be in serious danger if President Assad, Iran and Russia attack the province.

“There is a risk of a new humanitarian disaster. Idlib’s fate must be settled by a political process, which includes disarming the militias,” stated Mr. Le Drian.

The United Nations has also issued a statement on the matter, saying that a strike on Idlib would displace roughly 800,000 people and prevent Syrian war refugees from coming home.

United Nations Secretary-General António Guterres spoke on Wednesday saying that “any use of chemical weapons is totally unacceptable.” Guterres also added that he “urgently appeals to the Government of Syria and all parties to exercise restraint and to prioritize the protection of civilians.”

The United States’ national security adviser, John Bolton, also reported that the US will act strongly if Syrian President al-Assad were to use chemical weapons in the attack to re-take Idlib.

“We are obviously concerned about the possibility that Assad may use chemical weapons again,” said Bolton. “Just so there is no confusion here, if the Syrian regime uses chemical weapons we will respond very strongly,” added the national security adviser.

CNN reported that Assad’s regime has been moving helicopters closer and closer to Idlib province. The proximity of said helicopters has the United States concerned that another chemical attack may be underway.

Kremlin spokesman, Dmitry Peskov, however, responded to all warnings and said the Syrian army was currently “getting ready” for an offensive meant to eradicate a “cradle of terrorism” in the area.