Diplomats for the United States and Russia traded blame at a U.N. Security Council meeting Friday amid warnings that any U.S. strikes in response to a suspected chemical attack in Syria could lead to a larger regional and possibly global confrontation.

The U.S. ambassador to the United Nations, Nikki Haley, accused Russia of lying and covering up for its ally, the government of Syrian President Bashar al-Assad, which she said had used chemical weapons at least 50 times in the past seven years of warfare.

“Russia can complain all it wants about fake news, but no one is buying its lies and its coverups,” she said of Syria’s strongest ally. “Russia was supposed to guarantee Assad would not use chemical weapons, and Russia did the opposite.”

Haley’s Russian counterpart, Vassily Nebenzia, in turn accused the United States and its key allies France and Britain of bellicose rhetoric and saber-rattling that have heightened tensions.

Syrian President Bashar al-Assad is being accused of using chemical weapons to attack civilians in Douma, Syria, on April 7. (Jason Aldag/The Washington Post)

“Why are you seeking to plunge the Middle East into such difficulties, provoking one conflict after another, pitting one state against another?” he said, claiming that anti-government militias had received “instructions” to begin an offensive as soon as an act of force begins. “Is the latest wave of chaos being unleashed only for the sake of that?”

Just before the Security Council meeting began, Haley told reporters: “At some point, you have to do something. At some point, you have to say ‘enough.’ ”

Russia called for the emergency meeting on Syria as tensions remained high over a potential U.S. airstrike in response to last Saturday’s suspected chemical weapons attack that killed dozens in the town of Douma. The United States, France and Britain have said the Syrian government is most likely responsible for the deaths in Douma. Russia and Syria have both denied it.

Russian Foreign Minister Sergei Lavrov said April 11 Moscow has "undeniable evidence" that the suspected chemical weapons attacks in Syria were staged. (Reuters)

As the prospect of a U.S. strike loomed, the first team of investigators from the Organization for the Prohibition of Chemical Weapons arrived in Syria to look for evidence, with a second team expected soon.

U.N. Secretary General António Guterres told the Security Council that he feared events could escalate rapidly into a regional and even global conflict, and he urged all states “to act responsibly in these dangerous circumstances.”

One of the biggest questions concerning a potential U.S. strike on Syria is how Russia would react. The country is Assad’s most powerful ally and has thousands of troops and military advisers, as well as air defense systems, deployed in Syria.

Russia’s military has threatened to shoot down any U.S. missiles that put Russian lives at risk.

Russia also could fire at the launch platforms used — potentially U.S. planes or ships. Russian officials have said U.S. and Russian military staffs remain in contact regarding Syria, even as Russian media have carried stories in recent days about the potential outbreak of “World War III” as a consequence of a U.S. airstrike against Assad.

Russian President Vladimir Putin warned French President Emmanuel Macron in a phone call Friday that the situation remained tense, the Kremlin said in a statement.

“Most important, it is imperative to avoid badly planned and dangerous actions that would be crude violations of the U.N. Charter and would have unpredictable consequences,” the Kremlin said. “Both leaders directed the ministers of defense and foreign affairs to maintain close contact with the goal of de-escalating the situation.”

France’s U.N. ambassador, François Delattre, said the Syrian government’s decision to use chemical weapons meant that it had “reached a point of no return,” necessitating a “robust, united and steadfast response.”

Britain’s U.N. ambassador, Karen Pierce, noted that Prime Minister Theresa May’s cabinet “has agreed on the need to take action to alleviate humanitarian distress and to deter the further use of chemical weapons by the Assad regime.”

Announcement of that approval Thursday did not specify that the response should be military, although that was the expectation.

“We will continue to work with our friends and allies to coordinate an international response to that end,” Pierce said Friday.

Opposition lawmakers urged May to first seek Parliament’s consent before committing to any military action.

Meanwhile, the Russian Defense Ministry on Friday presented what it said was new evidence showing that Britain had staged the chemical attack. Maj. Gen. Igor Konashenkov, a ministry spokesman, alleged that a group of people, some with video cameras, had run into a hospital in the area and doused patients with water while shouting that there had been a chemical attack. Footage of the ensuing panic formed the evidence of the attack, Konashenkov said, according to the RIA Novosti state news agency.

Troianovski reported from Moscow. William Booth in London and Anne Gearan in Washington contributed to this report.