British police officers stand on duty as members of the Army work in a residential street in Alderholt, southern England, on March 15, 2018, as investigations and operations continue in connection with the major incident sparked after a man and a woman were apparently poisoned in a nerve agent attack in Salisbury on March 4. Britain expelled 23 Russian diplomats over the nerve agent poisoning of a former spy, and suspended high-level contacts, including for the World Cup, as the US joined it in blasting Moscow at the UN on March 14. British Prime Minister Theresa May told Britain's parliament that Russia had failed to respond to her demand for an explanation on how a Soviet-designed chemical, Novichok, was used in the English city of Salisbury on March 4. Pic/AFP

Russia has denied the existence of the Novichok programme, a military-grade nerve agent which Britain said was developed by Russia and had been used on its soil on March 4.