UN needs to investigate alleged Syria chemical attacks or US will act: Haley The U.S. wants to re-establish body to probe alleged chemical weapons attacks.

U.S. Ambassador to the United Nations Nikki Haley is urging the Security Council to adopt a resolution that condemns the reported chemical weapons attack in Syria over the weekend and would re-establish a U.N. investigative body to determine whether chemical weapons were used.

If the UN didn't act, Haley said, the U.S. would act on its own.

"Russia's obstructionism will not continue to hold us hostage when we are confronted with an attack like this one. The United States is determined to see the monster who dropped chemical weapons on the Syrian people held to account," she said, repeatedly calling Syrian strongman Bashar al-Assad a "monster."

Haley spoke in vivid detail about the attack, but said she wouldn't bother to hold up photos of the children murdered on Saturday, as she has before, because, "What would be the point? The monster who is responsible for these attacks has no conscience, not even to be shocked by pictures of dead children."

Neither does Russia, in her view, because "No civilized government would have anything to do with Assad's murderous regime," as Russia – Assad's ally and military backer – does. "Russia could stop this senseless slaughter if it wanted, but it stands with the Assad regime and supports without any hesitation," she added.

A draft of the resolution obtained by ABC News "condemns in the strongest terms the continued use of chemical weapons" in Syria – although it does not blame the Assad regime for the attack, instead establishing a U.N. "Independent Mechanism of Investigation" to try to determine whether chemical weapons were used and possibly who is responsible.

There was such a body, called the Joint Investigative Mechanism, or JIM, that reported last fall that Syrian strongman Bashar al-Assad's forces were responsible for a sarin gas attack in April 2017 that killed approximately 100 civilians and led to U.S. airstrikes on a Syrian military base. But Russia has since ended the JIM by blocking an extension of its mandate on numerous occasions.

The Russian permanent representative to the UN called the latest attack "fake news" during Monday's Security Council session and slammed the U.S., U.K., and France for their "slander, insults, hawkish rhetoric, blackmail, sanctions, and threats to use force against a sovereign state."

Ambassador Vasily Nebenzia argued that the attack was staged and said Russian specialists who went to the area took soil samples, "which showed the lack of nerve agent and chlorine-containing substances." They interviewed local residents, he said, and "Not a single local resident confirmed the chemical attack had taken place... There were no reports about symptoms from attacks from substance such as chlorine" at the local hospitals, he said.

In fact, he said, no bodies have been found – and without bodies, there could be no crime: "The bodies of the dead as result of the contamination were not found. Medical personnel and residents have no information about their potential burial areas. Thereby, the use of sarin and chlorine is not confirmed," he concluded.

The U.S. has disputed those claims, with a State Department official telling ABC News that victims' symptoms, "reported by credible medical professionals and visible in social media photos and video, are consistent with an asphyxiation agent and of a nerve agent of some type."

The U.N. body was briefed by the Deputy to the High Representative for Disarmament Affairs Thomas Markram and the Special Envoy of the Secretary-General for Syria Staffan de Mistura ahead of the open hearing. De Mistura, who has been special envoy for nearly four years, offered some of his starkest warnings yet about the increasingly complex conflict in Syria.

"The Council cannot allow a situation of uncontrollable escalation to develop in Syria on any front," the seasoned Italian diplomat said.

Markram, a South African diplomat, also urged the international body to take action: "The Council must fulfill its responsibilities. To do otherwise, or simply to do nothing, is to accept tacitly or otherwise that such a challenge is insurmountable. The use of chemical weapons cannot become the status quo," he said.

The Security Council will not be voting on the American resolution Monday. Instead, the U.S. has circulated it and now wants to negotiate with other Security Council members to pass it, a Security Council diplomat said.

It's also not an entirely new resolution, but one the U.S. has been trying to get passed for months now – updated with the news of this latest reported attack and modified with some of Russia's previous demands as a sign that the U.S. is willing to negotiate on this, the diplomat added.

Russian ambassador Nebenzia has already said, however, that it contains "some unacceptable elements," but it is unclear if they were willing to negotiate on it.

The apparent chemical attack on Saturday killed dozens of civilians, targeting a rebel enclave outside Damascus called Douma that has been pulverized by Assad's forces and his backers. U.S. intelligence is still assessing whether or not chemical weapons were used, a U.S. official said, but President Donald Trump has blamed "President Putin, Russia and Iran... for backing Animal Assad" in a tweet Sunday.

Ahead of a cabinet meeting midday Monday, he told reporters, "Nothing's off the table," including U.S. military actions, and his administration would make a decision in 24 to 48 hours.

Nebenzia warned against any U.S. military action, saying that armed force "under mendacious pretext" and with Russian troops in Syria, "could lead to grave repercussions."

But for the moment, Trump's administration is using diplomatic engagement as it works to try to get to the bottom of what happened in Douma -- and then decides what to do next, a State Department official told ABC News. They added that the U.N. Security Council is the focus right now, but pointed to other ongoing efforts, such as Trump's phone call with French President Emmanuel Macron and acting Secretary of State John Sullivan's call with British Foreign Secretary Boris Johnson.

Sullivan and Johnson agreed that "this attack bore hallmarks of previous chemical weapons attacks by the Assad regime," according to a British Foreign Office spokesperson. Johnson also spoke to his French counterpart Jean-Yves Le Drian on Monday as well, "underlin[ing] the importance of the UK, the US, and France remaining in close touch."

ABC News's Ben Gittleson and Luis Martinez contributed to this report.