A Syrian opposition group said renewed airstrikes hit the town of Khan Sheikhoun a day after the attack, which the Trump administration and others have blamed on the government of President Bashar Assad, as well as his main patrons, Russia and Iran.
Damascus and Moscow have denied they were behind the attack.
MORE: White House blames Obama administration for suspected Syria chemical attack
Russia's Defense Ministry said the toxic agents were released when a Syrian airstrike hit a rebel arsenal, an account Britain dismissed at an emergency U.N. session called in response to the attack.
British Ambassador Matthew Rycroft said the U.K. had seen nothing that would suggest rebels "have the sort of chemical weapons that are consistent with the symptoms that we saw yesterday."
Russia said it would submit information from its Defense Ministry to the Security Council debate.
A resolution drafted by Britain, France, and the U.S. stresses the Syrian government's obligation to provide information about its air operations, including the names of those in command of any helicopter squadrons on the day of the attack.
Diplomats were also meeting in Brussels for a major donors' conference on the future of Syria and the region. Representatives from 70 countries were present.
The attack on Khan Sheikhoun killed dozens of people on Tuesday, leaving residents gasping for breath and convulsing in the streets.
Videos from the scene showed volunteer medics using fire hoses to wash the chemicals from victims' bodies.
Haunting images of lifeless children piled in heaps reflected the magnitude of the attack, which was reminiscent of a 2013 chemical assault that left hundreds dead and was the worst in the country's six-year conflict.
The Turkish Health Ministry said three victims of the attack died while being treated in Turkey, and that 29 people wounded in the attack were still being cared for in hospitals in the country.
Syrian opposition groups had previously reported 72 dead.
Turkey set up a decontamination center at a border crossing in the province of Hatay following the attack, where the victims are initially treated before being moved to hospitals.
Syrian doctors said a combination of toxic gases is suspected to have been released during the airstrikes, causing the high death toll and severe symptoms.
The World Health Organization and the international medical charity Doctors Without Borders said victims of the attack appear to show symptoms consistent with exposure to a nerve agent.
In a statement, the agency said "the likelihood of exposure to a chemical attack is amplified by an apparent lack of external injuries reported in cases showing a rapid onset of similar symptoms, including acute respiratory distress as the main cause of death."
Pope Francis said during his general audience that he was "watching with horror at the latest events in Syria," and that he "strongly deplored the unacceptable massacre."
Earlier, President Donald Trump denounced the attack as a "heinous" act that "cannot be ignored by the civilized world."
German Foreign Minister Sigmar Gabriel called on Russia to endorse a planned Security Council resolution condemning the attack.
British Foreign Secretary Boris Johnson said "all the evidence" he had seen so far in the latest chemical weapons attack in Syria "suggests this was the Assad regime ... (that) did it in the full knowledge that they were using illegal weapons in a barbaric attack on their own people."
Syria's government denied it carried out any chemical attack. But early on Wednesday, Russia, a major ally of the Syrian government, alleged a Syrian airstrike hit a rebel arsenal, releasing the toxic agents.
The Russian Defense Ministry spokesman, Maj. Gen. Igor Konashenkov, said in a statement that Russian military assets registered the strike on a weapons depot and ammunition factory on the town's eastern outskirts.
Konashenkov said the factory produced chemical weapons that were used in Iraq.
Wednesday's renewed airstrikes hit near the location of the suspected chemical attack, said Ahmed al-Sheikho, of the Idlib Civil Defense team.
He said the strikes did not cause any casualties because the area had been evacuated following Tuesday's attack.
The Britain-based Syrian Observatory for Human Rights said 20 children and 17 women were among those killed. Abu Hamdu, a senior member of the Syrian Civil Defense in Khan Sheikoun, said his group has recorded 70 deaths.
He said his team of rescuers was still finding survivors, including two women and a boy hiding in an underground shelter beneath their home.
Israeli defense officials said Wednesday that military intelligence officers believed government forces were behind the attack.
The officials said Israel believes Assad has tons of chemical weapons currently in his arsenal. They spoke to The Associated Press on condition of anonymity Wednesday as they are not allowed to brief media.
Turkish President Recep Tayyip Erdogan also blamed the Syrian government for the attack.
A top Syrian rebel representative said he held U.N. mediator Staffan De Mistura "personally responsible" for the attack.
Mohammad Alloush, the rebels' chief negotiator at U.N.-mediated talks with the Syrian government, said the envoy must begin labeling the Syrian government as responsible for killing civilians.
He said the U.N.'s silence "legitimizes" the strategy.
"The true solution for Syria is to put Bashar Assad, the chemical weapons user, in court, and not at the negotiations table," said Alloush, who is an official in the Islam Army rebel faction.
Syria's rebels, and the Islam Army in particular, are also accused of killing civilians in Syria, but rights watchdogs attribute the overwhelming portion of civilian causalities over the course of the six-year-war to the actions of government forces and their allies.