MOSCOW — An international chemical weapons watchdog rebuffed Russia’s request Wednesday to join Britain’s investigation of the nerve-agent poisonings of an ex-spy and his daughter in England. Undeterred, Moscow next plans to take its denials of involvement to the UN Security Council.

Britain said Russia’s proposal for a joint investigation received only six votes at a special session of the executive council of the Organization for the Prohibition of Chemical Weapons. The council has representatives from 41 countries.

Russia requested the Wednesday session in The Hague, Netherlands, to push its repeated rejection of Britain’s allegation that Moscow was behind the March 4 poisonings of Sergei Skripal and his daughter, Yulia. The British government has invited experts from OPCW to help identify the substance that sickened the Skripals.

‘‘The purpose of Russia’s ludicrous proposal at The Hague was clear — to undermine the independent, impartial work of the international chemical weapons watchdog,’’ British Foreign Secretary Boris Johnson said in a statement.

Seeking a different international stage, Russia’s UN ambassador called for an open meeting of the UN Security Council on Thursday in the case that has chilled relations between Moscow and the West. Ambassador Vassily Nebenzia made the request at the end of his speech Wednesday to a council meeting on chemical weapons in Syria.

Nebenzia said Russia requested the council meeting because it shares the principle that the use of chemical weapons anywhere ‘‘is not acceptable and must be investigated and perpetrators punished, and that impunity is unacceptable.’’

Kuwait’s UN Ambassador Mansour Al-Otaibi told reporters the meeting is scheduled at 3 p.m. on Thursday.

At the special meeting in The Hague, Russia and Britain traded accusations of duplicity and untrustworthiness.

The British envoy said that a joint investigation, as proposed by Russia, would force ‘‘a victim to engage the likely perpetrator.’’

‘‘To do so would be perverse,’’ acting UK Permanent Representative John Foggo said, adding that Moscow’s demand showed ‘‘disdain.’’

Russia’s envoy to the international chemical weapons watchdog complained that Britain’s work with the agency has lacked transparency.

‘‘Russia, as well as other states that are members of the executive committee, have been pushed aside from this investigation,’’ Alexander Shulgin said during a news conference.

‘‘They tell us that they can inform us of the results of this investigation ... only with the good will of Great Britain,’’ Shulgin said. ‘‘But, knowing how our so-called partners have conducted themselves, we are not going to count on their good will.’’

The United States and many of Britain’s European allies have supported the UK in assigning blame for the poisonings to Russia.

Moscow has worked strenuously to undermine the allegation and pressured Britain to provide evidence backing its claim that Russia was responsible.

A spokeswoman for the Russian Foreign Ministry said Wednesday that Britain needed to provide information about the pets that lived in Sergei Skripal’s house in Salisbury, England.

‘‘Where are the pets? What is their condition?’’ ministry spokeswoman Maria Zakharova said. ‘‘This is about living creatures, and if a toxic chemical agent was indeed used in their house, these living creatures should have been hurt.’’

The chief of Britain’s defense research lab, the Porton Down laboratory, acknowledged Tuesday it has not been able to pinpoint the precise source of the nerve agent.

Gary Aitkenhead said scientists there identified the substance used on Sergei and Yulia Skripal as a Soviet-developed nerve agent known as Novichok.

But he added ‘‘it’s not our job to say where that was actually manufactured.’’

The British government says it relied on a combination of scientific analysis and other intelligence to conclude that the nerve agent came from Russia.

Britain is standing by its assessment, but the Foreign Office on Wednesday deleted a tweet from last month saying Porton Down scientists had identified the substance as ‘‘made in Russia.’’

Still, Russian President Vladimir Putin had quickly seized on Aitkenhead’s comments as proof that British accusations against Russia were baseless.