British Prime Minister Theresa May gave Russian President Vladimir Putin 24 hours to explain how a deadly Russian nerve agent was used in an assassination attempt on British soil, as she said it is "highly likely" Moscow was responsible.
May vowed Britain will pursue "extensive measures" unless a credible account can be given as to how military-grade Novichok was deployed, leaving an ex-spy, his daughter and a British policeman in hospital.
Meanwhile, a retaliatory action that might be announced as early as Wednesday could potentially include a larger military presence in Eastern Europe, fresh sanctions and action at the United Nations.
In this respect, British government sources told The Independent that UK ministers also discussed expelling the Russian Ambassador in response to what May branded a "reckless and despicable act".
May said if there is no "credible response" by the end of Tuesday, then the UK would conclude there has been an "unlawful use of force" by Moscow.
In parallel, May revealed experts at Britain's Porton Down defense laboratory have confirmed the Salisbury attack involved highly-specialized Novichok, first developed by the Soviet Union in the 1970s.
For his part, Putin dismissed claims about his state's alleged involvement on Monday, telling a BBC reporter who questioned him on a visit to a grain center: "We're dealing with agriculture here ... and you talk to me about some tragedies.
"Get to the bottom of things there, then we'll discuss this."
The Kremlin denied any involvement, while the Russian embassy accused Britain of playing a "very dangerous game" and warned of "serious long-term consequences" and Russian foreign ministry spokeswoman Maria Zakharova branded May' statement "a circus show in the British parliament".
Source: News Agencies, Edited by website team