Dozens of civilians, among them children, were killed and more than 200 were injured in an airstrike early Tuesday that released “toxic gas” on a town in northwest Syria.

The Britain-based Syrian Observatory for Human Rights, an opposition monitoring group, put the number of dead at 58, although unconfirmed reports said over 100 were killed.

The nature of the substance has yet to be confirmed, but a British doctor at the scene tweeted that the chemical released was sarin gas.

The Syrian Coalition, an opposition group based outside the country, said government planes carried out the airstrike on Khan Sheikhoun, south of the city of Idlib, the provincial capital. Rights groups have long accused President Bashar Assad of deploying chemical weapons against his own citizens.

The Syrian Observatory for Human Rights confirmed the deaths of 11 children from chemical exposure, but footage posted on Twitter showed some 20 young children lying motionless in a room.

Hours after the attack, a rocket slammed into a hospital as doctors treated victims, destroying part of the building, an AFP correspondent said. The projectile brought down rubble on top of medics as they struggled to deal with victims of the attack.

A wounded Syrian youth cries at a makeshift clinic following reported airstrikes by government forces in the rebel-held town of Douma, on the eastern outskirts of Damascus, on April 3, 2017. (Abd Doumany/AFP)

A wounded Syrian youth cries at a makeshift clinic following reported airstrikes by government forces in the rebel-held town of Douma, on the eastern outskirts of Damascus, on April 3, 2017. (Abd Doumany/AFP)

The province of Idlib is almost entirely controlled by the Syrian opposition. It is home to some 900,000 displaced Syrians, according to the United Nations. Rebels and opposition officials have expressed concerns that the government is planning to mount a concentrated attack on the crowded province.

There was no comment from the government in Damascus or any international agency on the attack.

Photos and video emerging from Khan Sheikhoun showed limp bodies of children and adults. Some are seen struggling to breathe; others appeared foaming at the mouth.

A medical doctor going by the name of Dr. Shajul Islam for fears for his own safety said his hospital in Idlib province received three victims, all with narrow, pinpoint pupils that did not respond to light. He published video of the patients on his Twitter account.

Pinpoint pupils, breathing difficulties, and foaming at the mouth are symptoms commonly associated with toxic gas exposure.

The activist-run Assi Press published video of paramedics carrying victims from the scene by a pickup truck. The victims were stripped down to their underwear. Many appeared unresponsive.

The Idlib Media Center published video of medical workers appearing to intubate an unresponsive man stripped down to his underwear and hooking up a little girl foaming at the mouth to a ventilator.

A January report drafted by the UN and the Organization for the Prohibition of Chemical Weapons determined for the first time that Assad and his younger brother Maher were tied to several chemical weapons attacks carried out in the country in 2014 and 2015.

In February, Human Rights Watch accused the Syrian government of conducting at least eight chemical attacks using chlorine gas on opposition-controlled residential areas during the final months in the battle for Aleppo last November and December.

Assad has claimed the bombings were to protect the Syrian people from rebels, whom he labels terrorists.

During a Friday press conference, White House Press Secretary Sean Spicer declared that the Trump administration wasn’t pursuing a strategy to push Assad out of power, making clear its focus is on defeating the Islamic State group.

He said the US approach was being driven by a new “reality” and that Assad’s future had to be a decision for the Syrian people.

Times of Israel staff contributed to this report.