U.S. President Donald Trump warned Wednesday that the Assad regime had crossed a line with its latest alleged chemical attack and faces a U.S. response.
Previously the White House has said its sole focus in Syria is defeating the Daesh terrorist group, not on ending Assad's civil war against opposition fighters.
But Trump and other senior U.S. officials said that the latest attack, which doctors say caused the agonizing deaths of at least 72 people, had changed the calculus.
He criticized his predecessor, Barack Obama, for drawing a "red line" on Syrian chemical weapon use, but failing to follow through when the line was crossed.
Trump indicated he does not want to telegraph U.S. strategy before taking action, having faulted Obama for doing so, and repeated Wednesday that Obama could have held Assad to account in 2013 when the former president laid down his red line on chemicals weapons use.
"It crossed a lot of lines for me," Trump said, at a joint White House news conference with Jordan's King Abdullah.
"When you kill innocent children, innocent babies, little babies ... that crosses many, many lines, beyond a red line, many, many lines," he warned.
"I will 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 a U.S. response to the atrocity will be -- and he has previously opposed deeper U.S. military involvement in Syria's civil war.
But his statement that his attitude had changed came after the U.S. ambassador to the United Nations, Nikki Haley, had warned of unilateral American action.
"When the United Nations consistently fails in its duty to act collectively, there are times in the life of states that we are compelled to take our own action," she said.