Russia's ambassador to the UK is to face questions from the British Foreign Secretary Boris Johnson over the Salisbury nerve agent attack.
The British Prime Minister Theresa May has told the House of Commons it was "highly likely" Russia was behind the incident that left Sergei and Yulia Skripal in a critical condition.
She stated that a military-grade nerve agent, developed by the Russians, was used.
Mrs May said answers were needed from the Russian government by midnight on Tuesday.
However, Moscow has denied the allegations, and has accused Britain of "making up new fairy tales".