On September 19, the first of two chemical weapons attacks in Syria took place.
The US-led coalition has been targeting the Syrian government for more than two years.
More than 1,000 civilians were killed in the attack on Khan Shaykhun, in the northwest of the country, which occurred during a rebel offensive in late August.
The Syrian government has denied responsibility for the attacks, which came just days after the US and its allies launched a military campaign against ISIS, a group that the Syrian opposition has accused of using chemical weapons.
In an interview with Al Jazeera English, Al Jazeera’s Middle East editor Azzam Rami, said the attack was one of the deadliest in Syria since the start of the war in 2011.
“We are now on the brink of an unprecedented escalation of the conflict.
We’re witnessing a new wave of the chemical weapons,” he said.
“The scale of this is far greater than anything we have seen before, and this is the first time that the US is publicly admitting that it has used chemical weapons.”
The use of chemical weapons is an issue for US President Donald Trump, who has repeatedly expressed a desire to eliminate them.
He has said the Syrian regime has “crossed a red line” by using chemical arms, and that the international community should “end this charade.”
Al Jazeera spoke to experts on chemical weapons at the University of Maryland and Johns Hopkins University who said that the chemical attack was likely the result of a US-backed attack on the Syrian military headquarters on August 21.
The two chemical agents were Sarin gas, a blister agent and a nerve agent.
The researchers said the Sarin was likely a blister that has a low toxicity and is designed to cause skin burns.
They also said that nerve agent was likely Sarin.
Both chemicals are considered highly toxic, with the US government placing the maximum death toll for Sarin at around 500 people.
The use of Sarin has led to concerns about the impact on the US military, as it has been blamed for thousands of deaths in Iraq, Afghanistan and Syria.
In the early hours of September 20, a US airstrike hit the Syrian headquarters of the Syrian Democratic Forces, a pro-government militia fighting ISIS.
The United States has been bombing the Syrian Arab Coalition, a coalition of several opposition groups, since late August, and the Syrian Republican Guard, a militia that the United States supports, also reported being hit by the US airstrike.
The Pentagon said the strikes targeted the SDF headquarters in al-Bab, which was used as the command centre of the coalition, and also damaged the SAA’s headquarters.
In response, the Syrian Air Force and its ally the Russian Air Force launched a massive attack on Raqqa, the de facto capital of the ISIS-held city of Raqqa.
The air force claimed that they were able to strike the command center of ISIS and hit several vehicles and weapons caches, although the exact location of the munitions remains unclear.
In Syria, the government’s offensive against ISIS and the military offensive against Assad’s forces have intensified, with Assad’s government conducting its first major offensive since the Syrian Civil War broke out in 2011 in the southern province of Deraa.
In mid-September, the United Nations and international agencies issued a joint statement that called for a ceasefire in Syria.
The statement said the US-Russia deal to end the conflict “has been the best chance for peace and reconciliation in Syria, and for the safe and orderly transition of power”.
The US, Russia and Iran have said that they would not agree to a ceasefire unless they receive clear assurances that Assad and his allies would abide by it.
On September 18, the US Department of State said that “it has concluded that Russia, Turkey, and Iran agree to an immediate cessation of hostilities in Syria and to the immediate implementation of the UN Security Council Resolutions.”
Russia and Turkey, along with Saudi Arabia, Qatar and the United Arab Emirates, have backed the Syrian rebels.
Al Jazeera was unable to confirm the veracity of the claim that Russia and the US were in “talks” to end hostilities in the country.
In a speech on September 24, Secretary of State Rex Tillerson said that Russia was not going to be part of a cease-fire in Syria until the UN and the International Criminal Court had “a serious and comprehensive investigation” into the use of weapons in Khan Shaykah.
He said that he had met with Russian Foreign Minister Sergey Lavrov and Russian Deputy Foreign Minister Mikhail Bogdanov on September 19.
The UN Human Rights Council also said on September 20 that it was investigating Khan Shaykat, adding that the investigation had begun “in the days leading up to” the attack.
The US has been pushing the international coalition to attack Syria since late September, after the attack in Khan Sheikhoun on August 19, and has been sending military advisers to Syria since that time.
The White House on September 16 announced that it would send a small number of military advisers