MOSCOW (Reuters) - Russia will only respond to a British demand it provide answers about the nerve agent that poisoned former double agent Sergei Skripal if London lets Moscow analyze the substance, Russian Foreign Minister Sergei Lavrov said on Tuesday.

British Prime Minister Theresa May said it was “highly likely” that Moscow was responsible for the poisoning in England of Skripal and his daughter using a military-grade nerve agent that was part of the Novichok group of nerve agents developed by the Soviet military.

Lavrov said the British government was obliged to provide Moscow access to the substance because Britain and Russia were signatories to the Chemical Weapons Convention.

But London had so far refused to provide Moscow access to the substance and other materials related to the poisoning case, Lavrov said.

“On these absolutely legitimate demands ... we received a gibberish response, which in general can be summarized by saying that we were denied these legitimate requests,” he said.

Britain should fulfill its international obligations under the Chemical Weapons Convention before Russia will respond to its request, Lavrov said.

“In general, speaking of manners, it must be remembered that the era of colonialism has for a long time been a thing of the past,” he said, commenting on May’s ultimatum to Moscow to explain the use of the nerve agent by the end of Tuesday.

Lavrov said Britain was handling the Skripal poisoning the same way it did the case of former KGB agent Alexander Litvinenko, who died in 2006 in London after drinking green tea laced with radioactive polonium-210. Britain alleged the Russian state was behind Litvinenko’s killing. Moscow denied involvement.

“We began to cooperate with the investigation (on the Litvinenko case), but it was classified and we were told that all information could not be provided to us,” said Lavrov.

“Now everything is beginning the same way: we are given nothing in response to our application,” Lavrov said.

Lavrov said Russia had no connection to Skripal’s poisoning and was ready to work together with the British authorities in line with the Chemical Weapons Convention.

“We have already made a statement that this is all nonsense ... We have no relation to it,” Lavrov said of British allegations of Russian involvement.