Photo shows a general view of a Security Council meeting on the poisoning of a former Russian spy, at the United Nations headquarters in New York, March 14, 2018. (Xinhua/Li Muzi)

UNITED NATIONS, March 14 (Xinhua) -- Russian ambassador to the United Nations Vasily Nebenzya said Wednesday that Britain's allegations that Moscow was responsible for a nerve attack were "completely unacceptable."

"The Russian Federation thinks it is completely unacceptable to launch unjustified accusations as contained in the letter from Theresa May dated March 13 to the Secretary-General of the United Nations," Nebenzya said at a UN Security Council emergency meeting regarding accusations of the use of a nerve agent in the United Kingdom on March 4.

"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," he added.

Britain's deputy UN ambassador Jonathan Allen said hundreds of his countrymen had potentially been exposed to the agent.

He said Sergei Skripal, a 66-year-old former Russian spy who became a double agent for Britain, and his 33-year-old daughter Yulia, were poisoned with "Novichok," which he insisted is a weapon that cannot be manufactured without the use of the highest-grade state laboratories.

"This was no common crime," he said. "It was an unlawful use of force."

U.S. ambassador to the UN Nikki Haley said that the Trump administration "stands in absolute solidarity with Great Britain" following the nerve agent attack against the former Russian spy and his daughter in the English city of Salisbury last week.

The United States believes that Russia "is responsible for the attack" on the two people using a military-grade nerve agent, Haley added.

Russia dismissed the accusations as "fairy tales" and denied any involvement in the attack.

Ma Zhaoxu, Chinese ambassador to the UN, said China hopes that "a comprehensive, objective and impartial investigation could be conducted based on facts and in accordance with relevant international rules and reach an evidence-based conclusion that can stand the test of facts and history."

"We hope relevant parties could properly handle this issue through appropriate channels," he said.

Sergei Skripal and his daughter were found slumped unconscious on a bench outside a shopping center in the southern English city of Salisbury on March 4. They remain in a critical condition.

British authorities have concluded that the two were poisoned with the nerve agent Novichok. London has demanded Moscow explain why the nerve agent that traces back to Russia should end up in Britain.

Prime Minister Theresa May announced Wednesday that her government will expel 23 Russian diplomats from Britain and will freeze Russian state assets "wherever we have the evidence that they may be used to threaten the life or property of UK nationals or residents."

Britain will also suspend all planned high-level bilateral contacts with Russia.

Russian Foreign Minister Sergei Lavrov on Wednesday denied his country's involvement in the poisoning incident.