After an emergency session of the UN Security Council on Wednesday, Western diplomats are expected to push for a vote as early as Thursday on a resolution demanding an investigation of the suspected attack.
French Foreign Minister Jean-Marc Ayrault said the resolution, presented by Britain, France and the United States, remained a priority.
"These crimes must not go unpunished," Ayrault told CNEWS television.
"It's difficult because up to now every time we have presented a resolution, there has been a veto by Russia and sometimes by China... but we must cooperate because we need to stop this massacre," he added.
Syria's regime and Russia hit back Thursday at accusations that Damascus was behind a deadly chemical weapons attack, as pressure built for international action over what Washington called an "affront to humanity".
France said it was determined to pursue a UN Security Council resolution to investigate dozens of civilian deaths in a northwestern Syria town, which Turkey said it suspected were the result of exposure to nerve agent sarin.
At least 86 people were killed early on Tuesday in rebel-held Khan Sheikhun, and dozens more have received treatment for convulsions, breathing problems and foaming at the mouth.
World powers have pointed the finger at the government of Bashar al-Assad, but Foreign Minister Walid Muallem repeated the government's denial on Thursday.
"The Syrian army has not, did not and will not use this kind of weapons -- not just against our own people, but even against the terrorists that attack our civilians with their mortar rounds," he said.
Russia also stood by its longtime ally, with President Vladimir Putin warning against a rush to judgement.
In a Kremlin statement, Putin underlined "the unacceptability of making unfounded accusations against anyone before a thorough and impartial international investigation is carried out."
More than 30 people were transferred across the border into Turkey for treatment following the incident, and Ankara said a preliminary probe found "a link between these injuries and the use of chemical weapons."
"According to the results of the initial analysis, the findings suggest the injured were exposed to a chemical substance (sarin)," the Turkish health ministry said in a statement.
Geert Cappelaere, Middle East regional director at UNICEF, the United Nations agency on children's issues, said Thursday that at least 27 children were killed in the suspected attack.
At least 546 people were wounded, he said, adding that "casualty figures are expected to rise".
If confirmed as an attack, it would be among the worst incidents of chemical weapons use in Syria's civil war, which has killed more than 320,000 people since it began in March 2011.
It has also prompted an about-face from US President Donald Trump, who in 2013 urged then-president Barack Obama not to intervene against Assad after a major suspected chemical attack.
Senior US officials had also recently suggested it was no longer a priority that Assad be removed from power.
Trump described the alleged attack as an "affront to humanity" and warned it had changed his view of Assad.
"I will tell you, it's already happened, that my attitude towards Syria and Assad has changed very much," he told reporters at a joint White House news conference with Jordan's King Abdullah.
"It crossed a lot of lines for me," he said, alluding to Obama's failure to enforce his own 2013 "red line" on the use of chemical weapons in Syria.
As she held up pictures of lifeless children at the UN on Wednesday, US ambassador Nikki Haley warned of unilateral action if the UN failed "in its duty to act collectively."
The draft UN resolution backs a probe by the Organization for the Prohibition of Chemical Weapons (OPCW) and demands Syria provide information on its operations.
On Thursday, Muallem said such an investigation "must guarantee that it is not politicised, that it has broad geographic representation and that it is launched from Damascus, not Turkey."
British ambassador to the UN Matthew Rycroft told reporters he hoped council members would agree on a draft resolution by Thursday, but vowed to press for a vote regardless.
Failure to agree on a compromise text could prompt Russia to use its veto to block the draft resolution, which Moscow has done seven times to shield Syria.
Syria officially relinquished its chemical arsenal and signed the Chemical Weapons Convention in 2013 to avert military action after it was accused of an attack outside Damascus that killed hundreds.
But there have been repeated allegations of chemical weapons use since.
Analysts said it was unclear whether the Trump administration would follow through with its threats of action.
"We're dealing with a real unknown here, in that we have no precedent to use to assess whether the Trump administration's words yesterday were bluster or a representation of genuine threat," said Charles Lister of the Middle East Institute.
"Trump... was exposed to the horrific footage that we all saw and quite clearly that had a transformative effect on him. Now we need to wait to see whether that transforms into real policy shifts or not."
*This story was editd by Ahram Online