NEW YORK — The US will respond to the Assad regime’s alleged chemical attack against Syrian civilians, US Ambassador Nikki Haley told the United Nations as she excoriated Russia, saying its hands are “covered in the blood of Syrian children.”

“Chemical weapons have once again been used on Syrian men, women and children,” Haley said at a special meeting of the United Nations Security Council to discuss what appeared to be a chemical attack on Douma, the last rebel-held town in Syria, on Saturday that left 49 people dead and scores injured.

“History will record this as the moment when the Security Council either discharged its duty or demonstrated its utter and complete failure to protect the people of Syria,” Haley said. “Either way, the United States will respond.”

Images of gasping children struggling to breathe shocked the world and galvanized President Donald Trump, who condemned the attack as “sick” and upbraided Russian President Vladimir Putin and Iran for supporting Syrian President Bashar al-Assad.

Trump threatened that there would be “a big price to pay” for the attack. Late Monday, the White House confirmed he’d spoken with French President Emmanuel Macron for the second time in two days.

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In a short, 28-word statement, the White House said “President Donald J. Trump spoke today with President Emmanuel Macron of France to continue their coordination on responding to Syria’s atrocious use of chemical weapons on April 7.”

At the UN, Haley reiterated Trump’s comments that Russia could “pay” as well, as divisions between Washington and Moscow were laid bare in the Security Council. Russia’s ambassador accused the US of plotting against Moscow and Syria, threatening international security, stoking global tensions and operating outside the confines of international law.

Haley described at length and in detail blue-skinned Syrian toddlers lying dead in their parents’ arms after the suspected chemical attack and made clear that the US sees Moscow as responsible. Russia, she implied, is not even a civilized nation.

“The monster who was responsible for these attacks has no conscience to be shocked by pictures of dead children,” Haley said, explaining that she wouldn’t show photos of the victims as she had after a chemical attack in April 2017 that led to US strikes on Syria.

“The Russian regime, whose hands are also covered in the blood of Syrian children, cannot be shamed by pictures of its victims,” she said. “We’ve tried that before.”

“Russia could stop this senseless slaughter, if it wanted,” she said. “But it stands with the Assad regime and supports it without hesitation. What’s the point of trying to shame such people? After all, no civilized government would have anything to do with Assad’s murderous regime.”

“Russia’s obstructionism will not continue to hold us hostage when we are confronted with an attack like this one,” she added.

Russia pushed back hard. “Nobody has invested you with the authority to act as gendarmes, policemen of the world … we call on you to return to the legal fold,” Ambassador Vassily Nebenzia said. Earlier, Russian Foreign Minister Sergey Lavrov had argued that there is no evidence chemical weapons were used, a claim Nebenzia echoed.

“The use of sarin and chlorine is not confirmed,” Nebenzia echoed in the Monday meeting. He went on to say that the US, along with the UK and France, is acting “without any justifications, and without considering the consequences have engaged in a confrontational policy toward Russia and Syria.”

In extended, rambling remarks, Nebenzia accused the US of plotting a strike against Damascus and planting the “fake news” of the Douma attack Saturday as justification. He then veered off onto the subject of an alleged nerve agent attack on a former Russian spy in the UK, attempting to link all the events.

“Is it not clear to all? Syria, Russia, Salisbury,” Nebenzia said, referring to the British city where the spy was poisoned.

The UK ambassador to the UN, Karen Pierce, pushed back against Nebenzia’s characterization that the UK, along with France, “blindly” follows the US and dismissed the Russian’s attempts to draw comparisons to the attack on the spy.

“We believe there is no legitimate reason not to support the call for this council to set up an independent investigative mechanism,” Pierce said. “We have nothing to hide, but it seems,” she said, that Russia, Syria, Iran and their supporters “have something to fear.”

Like the Russian envoy, Syria’s ambassador to the UN, Bashar Jaafari, attacked the US, its allies and UN humanitarian workers. He accused the US of creating “a big elephant of lies and deceit,” saying these lies were a precursor to some sort of attack against Syria.

The UN’s special envoy for Syria, Staffan di Mistura, noted that some states have publicly raised their suspicions that Syria was behind the attack. Other states, he said, “have strongly questioned the credibility of these allegations.”

“What reason more, then, for a thorough, independent investigation,” he concluded, as he denounced the use of chemical weapons as “abhorrent” and called for a thorough investigation.

Nongovernmental organizations on the ground had documented “hundreds of cases of civilians with symptoms consistent with exposure to chemical weapons,” he said.

Between August 2013 and February 2018 there have been at least 85 confirmed chemical attacks in Syria, with the Syrian government responsible for at least 50 of them, according to Human Rights Watch.

Even before Nebenzia’s accusations, Mistura warned about the hostilities in Syria spiraling out of control to threaten international stability. “I have reached a point in which I am expressing a concern about international security,” he told the council.

Telling the gathered officials that recent developments carry more danger than ever, he said that “different fault lines that are completely crossing each other and are interconnected” and escalation could “have absolutely devastating consequences that is difficult for us to even imagine.”

“The council cannot allow a situation of uncontrollable escalation in Syria on any front,” he said.

Haley and other speakers stressed that a dangerous precedent is being set.

“We are on the edge of a dangerous precipice,” Haley said. “The great evil of chemical weapons use that once unified the world in opposition is on the verge of becoming the new normal. The international community must not let this happen.”

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