Russia's ambassador to the United Nations calls for proof to be presented over Moscow's alleged involvement in the poisoning of a former spy in Britain.

"We demand that material proof be provided of the allegedly found Russian trace in this high resonance event. Without this, stating that there is incontrovertible truth is not something that we can take into account," said Vassily Nebenzia at a Wednesday UN Security Council meeting on the incident.

On March 7, British authorities announced that former double agent Sergei Skripal, 66, and his 33-year-old daughter, Yulia, had been hospitalized since they had been found unconscious on a bench outside a shopping center in the city of Salisbury. They were reportedly exposed to a nerve agent.

Skripal was found guilty by a Russian tribunal of selling classified information to Britain's spy agency MI6 and was imprisoned in Russia in 2006. He was exchanged in a spy swap in 2010.

Nebenzia added that on March 13, British Prime Minister Theresa May sent a letter to the UN secretary general in which she made claims over Russia's involvement and its use of toxic agents in the Salisbury incident.

"We were given an ultimatum and requested in 24 hours to admit that we committed a crime... We do not speak the language of ultimatums. We do not use that language with anyone. And we will not allow to be spoken to in that language either. But we are polite. And on the 13 of March we did send a note to the Foreign Office where we reaffirmed that we had nothing to do with this incident," added Nebenzia.

US believes Russia responsible for attack

Nebenzia's remarks came shortly after US Ambassador to the United Nations Nikki Haley told the Security Council that Russia had a hand in the Salisbury incident.

US Ambassador to the United Nations Nikki Haley (C) arrives for a Security Council session after the the UK called for an urgent meeting to update council members on an investigation into a recent nerve agent attack in Salisbury, March 14, 2018.

"The United States stands in absolute solidarity with Great Britain. The United States believes that Russia is responsible for the attack on two people in the United Kingdom using a military-grade nerve agent," she said.

"Russia must fully cooperate with the UK's investigation and come clean about its own chemical weapons program. Russia is a permanent member of the Security Council. It is entrusted in the United Nations Charter with upholding international peace and security. It must account for its actions," she added.

UK: Highly likely Russia responsible for attack

UK Deputy Ambassador to the UN Jonathan Allen also told the council that his government had no choice but to believe that Russia was responsible for the attack.

UK Deputy Ambassador to the United Nations Jonathan Allen speaks at the Security Council after the UK called for an urgent meeting to update council members on an investigation into a recent nerve agent attack in Salisbury, March 14, 2018.

"We have concluded that Mr. Skripal and his daughter were poisoned with Novichok, a military-grade nerve agent of a type developed by Russia. It is not a weapon which can be manufactured by non-state actors. It is so dangerous that it requires the highest-grade state laboratories and expertise," he said.

UK media reports have likened the alleged poisoning to the assassination of Alexander Litvinenko, another Russian agent killed in Britain in 2006 with radioactive material that was purportedly put in his cup of tea by Russian agents.

"Based on the knowledge that Russia has previously produced this agent, and combined with Russia's record of conducting state-sponsored assassinations, including against former intelligence officers whom they regard as legitimate targets, the UK government concluded that it was highly likely that Russia was responsible for this reckless act," he added.

Kremlin spokesman Dmitry Peskov has repeatedly denied any involvement in the poisoning of the double spy in Britain. Peskov said the fact that the attack took place in England proves Russia had no role in the incident.

The UNSC meeting was held after the UK announced that plans to expel 23 Russian diplomats over the attack on the former Russian double spy.