BEIRUT: Western powers pushed ahead Thursday with efforts to take action over the suspected chemical attack in Syria after US President Donald Trump warned the "affront to humanity" would not go unanswered.
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 blamed Thursday on a "chemical attack" by the Damascus government.
President Bashar al-Assad's army has categorically denied that it used chemical weapons on Khan Sheikhun, and its ally Russia said "toxic substances" may have been released when Syrian troops struck a "terrorist warehouse".
At least 86 people were killed early on Tuesday in the rebel-held town, and dozens more have received treatment for convulsions, breathing problems and foaming at the mouth.
An AFP correspondent in Khan Sheikhun on Wednesday said the town was reeling, with dead animals lying in the streets and residents still shell-shocked after watching their entire families die.
"Nineteen members of my family were killed," 28-year-old Abdulhamid said in the town, surrounded by mourning relatives.
"We put some masks on but it didn't do anything... People just started falling to the ground," said Abdulhamid, who lost his twin children and wife in the attack.
Ankara said autopsies of three people transferred to Turkish hospitals confirmed that chemical weapons had been used.
'Must not go unpunished'
"This scientific investigation also confirms that Assad used chemical weapons," Justice Minister Bekir Bozdag told Turkish state media.
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.
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 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.
"I will tell you, it's already happened, that my attitude towards Syria and Assad has changed very much," Trump 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.
Trump did not go into detail about what any US response would be, and he has previously opposed deeper US military involvement in Syria's civil war.
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."
US Secretary of State Rex Tillerson, who is due in Moscow next week, told reporters there was "no doubt" that Assad's government was responsible for the attack.
"And we think it is time for the Russians to really think carefully about their continuing support for the Assad regime."
'Gas so lethal'
The draft resolution backs a probe by the Organization for the Prohibition of Chemical Weapons (OPCW) and demands Syria provide information on its operations.
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.
Russia turned up at negotiations with a rival draft resolution that made no reference to specific demands that Damascus cooperate with an inquiry, diplomats said.
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.
Doctors said victims showed symptoms consistent with the use of a nerve agent such as sarin -- suspected to have been used by government forces in the 2013 attacks.
US officials have not said what kind of agent they think was used, but Trump said it was "a chemical gas that is so lethal, people were shocked to hear what gas it was."