The dead were still being identified, and some humanitarian groups said as many as 100 had died.
Western leaders including President Donald Trump blamed the Syrian government of President Bashar Assad and called on its patrons, Russia and Iran, to prevent a recurrence of what many described as a war crime.
Dozens of people, including children, died — some writhing, choking, gasping or foaming at the mouth — after breathing in poison that possibly contained a nerve agent or other banned chemicals, according to witnesses, doctors and rescue workers. They said the toxic substance spread after warplanes dropped bombs in the early morning hours. Some rescue workers grew ill and collapsed from proximity to the dead.
The opposition-run Health Department in Idlib province, where the attack took place, said 69 people had died, providing a list of their names. The dead were still being identified, and some humanitarian groups said as many as 100 had died.
The government of Assad, who renounced chemical weapons nearly five years ago after a large chemical attack that U.S. intelligence agencies concluded was carried out by his forces, denied that his military had been responsible, as he has done every time chemical munitions have been used in Syria.
A statement from the Syrian military accused insurgents of responsibility and said they had accused the army of using toxic weapons “every time they fail to achieve the goals of their sponsors.”
But only the Syrian military had the ability and the motive to carry out an aerial attack like the one that struck the rebel-held town of Khan Sheikhoun.
Russia offered another explanation. A spokesman for its Defense Ministry, Maj. Gen. Igor Konashenkov, said Syrian warplanes had struck an insurgent storehouse containing toxins to be used in chemical weapons.
Witnesses to the attack said it began before 7 a.m. Numerous photographs and graphic videos posted online by activists and residents showed children and older adults gasping and struggling to breathe, or lying motionless in the mud as rescue workers ripped off victims’ clothes and hosed them down. The bodies of at least 10 children lay lined up on the ground or under a quilt.
A few hours later, according to several witnesses, another airstrike hit one of the clinics treating victims, who had been sent to smaller hospitals and maternity wards because the area’s largest hospital was severely damaged by an airstrike two days earlier.
The scale and brazenness of the assault threatened to further subvert a nominal and often violated cease-fire that had taken hold in parts of the country since Assad’s forces retook the northern city of Aleppo in December with Russian help, emboldening the Syrian leader to think he could win the war.
The attack also seemed likely to dampen peace talks that have been overseen by the United Nations in Geneva and by Russia and Turkey in Astana, Kazakhstan.
Incredulous over the chemical assault, humanitarian groups demanded action from the U.N. Security Council, where partisan divides over who is to blame for the Syrian war have paralyzed its members almost since the conflict began in 2011.
On Tuesday night, Britain, France and the United States were pushing the Security Council to adopt a resolution that condemns the attack and orders the Syrian government to provide all flight logs, flight plans and names of commanders in charge of air operations, including those for Tuesday, to international investigators.
The draft resolution, negotiated among diplomats from the three countries on Tuesday, was later circulated to all 15 members of the council. It could come up for a vote as early as Wednesday.
For Trump, who has repeatedly blamed what he has called President Barack Obama’s failures for the Syria crisis, the chemical weapons assault posed a potential policy dilemma and exposed some attack near Damascus that U.S. intelligence attributed to the Syrian military killed more than 1,400 civilians, including hundreds of children, according to U.S. government estimates at the time. “President Obama, do not attack Syria,” Trump said on Twitter. “There is no upside and tremendous downside.”
Trump’s administration, which would like to shift the focus in Syria entirely to fighting the Islamic State, has in recent days described Assad’s hold on his office as a political reality — an assertion that has drawn strong condemnation from influential Republicans who say Assad must leave power.
Secretary of State Rex W. Tillerson, who had said that Assad’s fate “will be decided by the Syrian people,” struck a sharply different tone on Tuesday, urging Assad’s allies Russia and Iran “to exercise their influence over the Syrian regime and to guarantee that this sort of horrific attack never happens again.”
Tillerson added that “Russia and Iran also bear great moral responsibility for these deaths.”
Russia has insisted that it had no military role in the strike. But a State Department official who briefed reporters in Washington said Russian officials were trying to evade their responsibility because Russia and Iran were guarantors of the Assad government’s commitment to adhere to a cease-fire in the peace talks that the Kremlin had helped organize in Astana.
Rescue workers from the White Helmets civil defense organization said that many children were among the dead and wounded. Radi Saad, who writes incident reports for the group, said that volunteers had reached the site not knowing a chemical was present and that five of them had suffered from exposure to the substance.