Russia’s ambassador to the United Nations on Thursday denounced allegations that the Kremlin was behind the poisoning of an ex-spy in Britain last month, calling the suspicions an attempt to “discredit and delegitimize” Russian involvement in countries such as Syria.

In a special meeting of the Security Council called by Russia, Vassily Nebenzia asserted that “with a high degree of probability,” the intelligence services of other countries are behind the March 4 poisoning of the former Russian double agent, Sergei Skripal, and his daughter in the English country town of Salisbury.

“This is a coordinated, very well-planned campaign” aiming to undermine Russia’s role “not only in finding a solution in Syria, but anywhere else,” Nebenzia said.

The British government has concluded that it is “highly likely” that the Kremlin poisoned Skripal, who remains in critical condition. But scientists at the British lab that analyzed samples said they could not pinpoint its origin, only that it was a military-grade nerve agent in the Novichok family.

The poisoning led more than 20 countries, including the United States, to expel about 150 Russian intelligence officers posing as diplomats, in a coordinated show of solidarity with London.

Russia called the Security Council meeting after the Organization for the Prohibition of Chemical Weapons, a watchdog group based at The Hague, on Wednesday rejected Moscow’s bid to join its investigation.

Nebenzia opened the session with lengthy, wide-ranging remarks in which he raised serious questions about the nerve agent’s origin and posed more-off-the-wall questions such as what happened to the Skripals’ pet cats and guinea pigs.

He tried to undercut suspicions that the Kremlin is the only plausible perpetrator, warning Britain’s ambassador, Karen Pierce, “You’re playing with fire, and you’ll be sorry.”

“Novichok is not copyrighted by Russia in spite of the obviously Russian name,” said Nebenzia, adding that the United States and Britain also had developed the nerve agent.

Nebenzia belittled some of the theories British officials have put forward, at one point reading from “Alice in Wonderland” in a display of nonsensical allegations.

Pierce in turn said Moscow was trying to deflect blame with a wide net, postulating theories that blamed terrorists and other groups or suggesting it was an attempt to distract from Brexit, Britain’s departure from the European Union. She compared Russia’s offer to participate in the investigation to an arsonist wishing to investigate the fire he had set.

British authorities have conveyed Russia’s desire to have its consul visit Skripal’s daughter, Yulia, who is recovering from the poisoning. Pierce said it will be her decision.

Kelley Currie, the U.S. deputy ambassador, accused Russia of peddling conspiracy theories that she dubbed “preposterous.”

“We firmly believe Russia is responsible for this chemical weapons attack on British territory,” she said. “Either Russia deliberately used this chemical weapon or failed to secure its stocks.”

Earlier in the day, at a conference on international security in Moscow, Russian Foreign Minister Sergei Lavrov dismissed the accusations of Russian culpability as a “fairy tale.”

Lavrov called for a “substantial and responsible” probe into the poisoning case and said Russia wants to “establish the truth” about what happened.

Lavrov said the refusal to allow Russia to join the investigation was a “mockery of international law, diplomatic etiquette and elementary decency.” He said Skripal’s poisoning was “staged to justify the expulsion of so many diplomats.”