The United States and Russia were on a collision course over Syria on Wednesday after a horrific chemical attack so shocked President Donald Trump that Washington threatened unilateral US action.
At least 86 people were killed early on Tuesday in rebel-held Khan Sheikhun in northern Syria and dozens more were being treated after they were found convulsing and foaming at the mouth.
After previous major chemical attacks in Syria in 2013, Trump strongly urged then-president Barack Obama not to order military intervention against Bashar al-Assad's regime.
And he came to office promising both to improve ties with Assad's ally President Vladimir Putin of Russia and tofocus US efforts in Syria solely on the defeat of the Islamic State group.
But on Wednesday -- as footage emerged of Syrian childrenchoking to death in agony -- he declared that his view of the conflict had been changed by an attack that "cannot be tolerated."
"It crossed a lot of lines for me," Trump told reporters at a joint White House news conference with Jordan's King Abdullah, alluding to Obama's failure to enforce his own 2013 "red line."
"When you kill innocent children, innocent babies, little babies... that crosses many, many lines, beyond a red line, many, many lines," he warned.
"Iwill tell you, it's already happened, that my attitude towards Syria and Assad has changed very much... You're now talking about a whole different level."
Trump did not go into detail about what any US response to the atrocity would be -- and he has previously opposed deeper US military involvement in Syria's civil war.
TheUS ambassador to the United Nations, Nikki Haley, warned of unilateral action and Secretary of State Rex Tillerson urged Russia to rethink its support for Assad.
The warning came during an emergency meeting of the UN Security Council called by France and Britain after the attack.
Britain, France and the United States have presented a draft resolution demanding a full investigation of the attack.
Russia-- along with Iran -- is Syria's main diplomatic and military partner. And Moscow, true to form, said the draft text was "categorically unacceptable."
Failure to agree on a compromise text could promptRussia to use its veto to block the draft resolution. Moscow has used its veto seven times to shield Syria from UN action.
Doctorssaid victims showed symptoms consistent with the use of a nerve agent such as sarin -- suspected to have been used by government forces in deadly attacks outside Damascus in 2013.
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."
If confirmed, the attack would be among the worst incidentsof chemical weapons use in Syria's civil war, which has killed over 320,000 people since it began in March 2011.
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.