The UK is freezing high-level contacts with Russia, expelling 23 Russian diplomats believed involved in espionage-related activities and cancelling the visit of Russian Foreign Minister Sergei Lavrov to London, British Prime Minister Theresa May said in the Parliament on Wednesday.

May repeated the conclusion of British investigators that Russia had either deployed or lost control of dangerous nerve agent used in the attack. She added Russia's defiant response has "demonstrated complete disdain for the gravity of these events."

"Instead they have treated the use of a military grade nerve agent in Europe with sarcasm, contempt and defiance," she told lawmakers while announcing the reprisal measures.

May said Russia has provided no convincing explanation about the deadly chemical attack against a former double agent in Salisbury last week. She said the UK government has concluded Russia "bears responsibility" for poisoning of former Russian spy Sergei Skripal and his daughter Yulia.