The UK and Russia are heading for a political showdown over the nerve agent attack on ex-spy Sergei Skripal on British soil.
66-year-old Skripal and his daughter Yulia fell victims to a nerve agent attack on March 4 in Salisbury. They both remain in a critical condition in hospital.
The toxic substance used was found to belong to the Novichok family of nerve agents, which were developed in the 1970s-1980s in the then Soviet Union. There are at least 100 known variants with various degrees of potency.
British Prime Minister Theresa May set a deadline for Moscow to provide an explanation of how and by whom was Sergei Skripal attacked, but the deadline passed unheeded.