The Security Service of Ukraine (SBU) has banned from entry to 23 Russian citizens involved in the intelligence services of the Russian Federation who were expelled from the UK in connection with the poisoning of former employee of the Russian Federal Security Service Sergei Skripal and his daughter.

"The SBU Chief Vasyl Hrytsak noted that their [Russians'] activity is a daring mockery of one of the key functions of the diplomatic mission defined by the Vienna Convention on Diplomatic Relations dated 1961 - the encouragement of friendly relations between states," the press service of the SBU said on Tuesday evening.

Focusing on Ukraine's experience in countering the hybrid aggression of the Russian Federation, Hrytsak stressed that Russian intelligence agents, under the guise of diplomats, increasingly resort to cynical provocations aimed at undermining the foundations of international stability and security.

As reported, Skripal and his daughter were poisoned with an unknown substance near a shopping center in Salisbury, the UK, on March 4. They are still in a coma. According to British detectives, the two were affected by the Novichok nerve gas allegedly designed in Russia.

British Prime Minister Theresa May laid the blame for the poisoning on Russia and announced measures to be taken against Russia in connection with this case.

In particular, May announced that London decided to send 23 Russian diplomats in connection with the poisoning in Salisbury of former intelligence officer Skripal and his daughter.

In addition, the UK will freeze Russian state assets in case their use is proven against the security of the United Kingdom, May added. She also said that a "number of secret measures" could be adopted against Russia.

May said that as part of the response to Russia in connection with the "Skripal case", London recalled its invitation to Lavrov to visit the country with a return visit, which had been handed after the visit of British Foreign Minister Boris Johnson to Moscow.

May said about the strengthening of checks of Russian citizens and private aircraft on the borders of the kingdom. "In response to the incident with Skripal, the UK will strengthen customs checks and control of private aircraft," she said, speaking to British parliamentarians.

Moscow dismissed all allegations of its involvement in the Skripal case and said it destroyed the entire arsenal of chemical weapons in 2017.

On march 27, following the UK's actions, twenty-three countries announced the expulsion of Russian diplomats in connection with the Skripal case. Some 114 Russian diplomats will be expelled from 16 countries of the European Union, as well as the United States, Canada, Albania, Macedonia, Norway, Ukraine, and Australia.