The death toll from a suspected chemical weapons attack in northern Syria has risen to 86, a monitoring group said.
The UK-based Syrian Observatory for Human Rights said those killed in Tuesday's attack on the town of Khan Sheikhoun included 30 children and 20 women.
Earlier, US President Donald Trump denounced the attack as an "affront to humanity".
A Syrian opposition group said renewed air strikes had hit 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.
Mr Trump said the attack crossed "many, many lines" and cannot be tolerated.
He said: "That attack on children yesterday had a big impact on me. Big impact. My attitude towards Syria and Assad has changed very much."
Mr Trump refused to reveal what action the US might take in response, saying disclosing military action ahead of time was a mistake the Obama administration had repeatedly made.
"I'm not saying I'm doing anything one way or another, but I'm certainly not going to be telling you," he said.
Mr Trump said the attack was "so horrific" and noted that it had killed "innocent people, small children and even beautiful little babies".
"These heinous actions by the Assad regime cannot be tolerated," he said.
Damascus and Moscow denied they were behind the attack.
Russia's defence ministry said the toxic agents were released when a Syrian air strike hit a rebel arsenal, an account Britain dismissed at an emergency UN session called in response.
British Ambassador Matthew Rycroft said the UK 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 defence ministry to the Security Council debate.
A resolution drafted by Britain, France, and the US 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, 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.
The attack 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 had died.
Turkey set up a decontamination centre 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 air strikes, causing the high death toll and severe symptoms.
The World Health Organisation and the international medical charity Doctors Without Borders said victims of the attack appeared 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, 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.
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