Donald Trump has described the chemical attack in Idlib province which killed more than 70 people as an “affront to humanity”, but offered little clue to any new strategy to end the violence in Syria.

The US president said that Tuesday’s attack – whose victims included women, children and babies – had affected him profoundly and transformed his thinking about the Syrian president, Bashar al-Assad.



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“I will tell you that attack on children yesterday had a big impact on me – big impact,” Trump said in the White House Rose Garden. “My attitude toward Syria and Assad has changed very much … You’re now talking about a whole different level.”



But during a joint press conference with King Abdullah of Jordan on Wednesday, Trump also repeated his criticism of Barack Obama’s administration for drawing and then failing to enforce a “red line” over Assad’s use of chemical weapons.

“I think that set us back a long ways, not only in Syria but in many other parts of the world because it was a blank threat,” Trump said, acknowledging that he now carried responsibility for the crisis.

Obama and his officials have disputed this criticism, insisting that they struck a deal with Russia to remove Syria’s weapons of mass destruction without a need for military intervention.

Facebook Twitter Pinterest Syrian children receive treatment at a hospital following a suspected toxic gas attack in Khan Sheikhun. Photograph: Mohamed Al-Bakour/AFP/Getty Images

When asked if the chemical weapons attack on Khan Sheikhun had crossed a red line, Trump said: “It crossed a lot of lines for me. When you kill innocent children, innocent babies, babies, little babies, with a chemical gas that is so lethal – people were shocked to hear what gas it was. That crosses many, many lines, beyond a red line, many, many lines.”

Pressed whether he would consider military intervention to remove Assad, the US president replied: “I’m not saying I’m doing anything one way or another, but I’m certainly not going to be telling you … Militarily, I don’t like to say where I’m going and what I’m doing.”

The British prime minister, Theresa May, currently in Saudi Arabia, said the UK would call for the Organisation for the Prohibition of Chemical Weapons to investigate. “I’m very clear there can be no future for Assad in a stable Syria, which is representative of all the Syrian people and I call on all the third parties involved to ensure that we have a transition away from Assad,” she said. “We cannot allow this suffering to continue.”

Earlier, Trump’s ambassador to the United Nations, Nikki Haley, warned Russia it “cannot escape responsibility” for the attack. Addressing the security council, Haley said it was clear that Assad, Russia and Iran had “no interest in peace”.

The emotive speech, during which Haley stood up to display pictures of children killed in the attack, was as harsh in tone as anything delivered in the same forum by her predecessor, Samantha Power.

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In contrast, the US secretary of state has remained largely silent regarding the attack. Rex Tillerson issued a statement critical of the Assad regime and Russia on Tuesday evening but dodged an opportunity to make his point in person in front of cameras.

But it is far from clear how much sway either Haley or Tillerson has on foreign-policymaking in an administration being rocked by a power struggle among White House factions.

Last week, Haley said removing Assad was no longer a US priority, in line with the White House emphasis on attacking Islamic State (Isis).

But on Wednesday, Haley suggested that if the UN security council remained deadlocked on responding to war crimes in Syria, the US might act unilaterally somehow to stop further chemical attacks by the Assad regime.

“When the UN consistently fails in its duty to act collectively, there are times in the life of states when we are compelled to take our own actions,” she said.

Like Trump, she did not say what kind of action the US and its allies might take.

Haley spoke immediately after the deputy Russian envoy, Vladimir Safronkov, who claimed that a Syrian regime airstrike on an opposition warehouse had hit a rebel chemical weapons facility.

Haley was scathing in her rejection of the Moscow version of events, and noted that the investigation that had been set up by the security council had found clear evidence that the Syrian regime was responsible for earlier chemical weapon attacks.

“Time and time again, Russia uses the same false narrative to deflect attention from their allies in Damascus,” Haley said. “Time and time again, without any factual basis, Russia attempts to place blame on others.”

Safronkov had suggested the timing of Tuesday’s attack was intended to disrupt Russian-led peace talks in Astana, Kazakhstan. Haley responded by saying that real progress toward a peaceful settlement was being undermined by the Syrian regime and its backers.

She added: “There is an obvious truth here that must be spoken. The truth is that Assad, Russia and Iran have no interest in peace.”

Speaking in Brussels, where he is attending an international aid conference, the British foreign secretary, Boris Johnson, said all the evidence pointed to the responsibility of the Assad regime and stepped up calls for a political transition in Syria, without specifying how this might happen.

“Objectively, I simply don’t see how Bashar al-Assad can remain in charge after what he has already done,” the foreign secretary said. “Of the 400,000 who are estimated to have been killed in Syria, he is responsible for the vast majority of that butcher’s bill. And you have to go a long way back in history to find a tyrant who has stayed in office given such circumstances.”

Johnson called on all members of the UN security council to support a resolution, drafted by the UK and France, denouncing the chemical weapons attack.

“I hope absolutely everyone feels able to support it, because all we are saying is that there should be condemnation of that chemical weapons attack, and secondly that there should be a thorough and urgent international investigation. And I don’t think anybody could possibly, reasonably oppose such a resolution in all conscience.”

The Turkish leader, Recep Tayyip Erdoğan, a staunch critic of Assad for much of the war, condemned him and the international community and described those who had been killed as “martyrs due to chemical weapons”.