According to a letter from British national security adviser Mark Sedwill to the secretary general of the United Nations, Russia has been training special units in ways to carry out chemical attacks, including applying chemical agents to door handles.
Mr. Sedwill’s letter, the most detailed account of British intelligence on the subject to be shared with the public to date, also reported that President Vladimir V. Putin of Russia was “closely involved in the chemical weapons program” beginning in the mid-2000s.
During that period, the letter claims, Russia was secretly developing the nerve agents known as Novichok that British officials say were used in the March 4 attack on Sergei V. Skripal and his daughter, Yulia, in the quiet cathedral city of Salisbury, England.
Russia has repeatedly denied both the attack on the Skripals, saying it no longer possesses Novichok or other chemical agents.
In a news conference Friday afternoon, the Russian ambassador to Britain, Aleksandr V. Yakovenko, dismissed the letter and “all these allegations” surrounding the nerve agent attack as having “nothing to do with reality.”
Russia, he said, repeating a claim the Kremlin has asserted throughout the Skripal affair, eliminated all of its stockpiles of chemical weapons in 2017, and as for Novichok, “We did not produce it and didn’t store it.”
Sedwill also states in the letter that British authorities believe Skripal was being monitored by Russian security services and that his email was hacked by Russia’s Foreign Intelligence Services in 2013.
“We therefore continue to judge that only Russia has the technical means, operational experience and motive for the attack on the Skripals, and that it is highly likely that the Russian state was responsible,” the letter said. “There is no plausible alternative explanation.”
It goes on to say that “during the 2000s,” Russia created a special unit to develop chemical weapons for use as tools in state-sponsored attacks and to “train personnel from special units in the use of these weapons.”
“This program subsequently included investigation of ways of delivering nerve agents, including by application to door handles,” it said. “Within the last decade, Russia has produced and stockpiled small quantities of Novichoks under the same program.”