The former spy, Sergei V. Skripal, and his daughter, Yulia, were poisoned on March 4 with what British investigators have identified as Novichok, a potent nerve agent developed in the Soviet Union in the 1970s and 1980s.
Russia has denied any connection to the poisoning.
The nerve agent “is not a weapon that can be manufactured by nonstate actors,” Mr. Allen said. He accused Russia of maintaining supplies of the agent, despite declaring in 2017 that it had destroyed all of its chemical weapons stockpiles.
“A weapon so horrific that it is banned from use in war was used in a peaceful city in my country,” Mr. Allen said.
The Security Council session appeared to be part of a broad effort by the British government to marshal the support of allies for a robust response to Russia. Hours earlier, Britain’s prime minister, Theresa May, expelled 23 Russians she said were spies and suspended high-level contacts between Moscow and London.
Despite the deepening diplomatic crisis, it was not clear what further action the British could take to penalize Russia at the United Nations. As a permanent member of the Security Council, Russia could veto any resolution intended to punish it.
Past efforts to hold Russia accountable for international misdeeds — the poisoning of a former spy in London in 2006 with a radioactive isotope, or the downing of a passenger plane over Ukraine in 2014 — went almost nowhere.
Judging by the reactions of Russian officials and government-run news media to the latest accusations, few expect to face serious consequences this time.
After Mr. Allen and Ms. Haley had spoken, Russia’s ambassador, Vasily A. Nebenzya, responded with mockery and sarcasm. He accused the British government of acting like Inspector Lestrade, the hapless detective from the Arthur Conan Doyle novels who is constantly upstaged by Sherlock Holmes.
Ms. Haley, meanwhile, was clearly “an experienced chemist” to be so certain of her conclusions, Mr. Nebenzya said.
Then he suggested that Britain had the most to gain from the poisoning by using it in a “black P.R.” campaign to harm Moscow’s reputation ahead of the 2018 World Cup, which Russia is hosting in three months.
“The authorities of the United Kingdom are constantly trying to tarnish Russia,” he said.
In her remarks, Ms. Haley acknowledged that Russia’s behavior is a frequent topic for the United States and its allies at the United Nations.
“We take no pleasure in having to constantly criticize Russia,” she said. “But we need Russia to stop giving us so many reasons to do so.”