Inspectors from the Organisation for the Prohibition of Chemical Weapons (OPCW) arrive to begin work at the scene of the nerve agent attack on former Russian agent Sergei Skripal, in Salisbury, Britain March 21, 2018. REUTERS/Peter Nicholls

MOSCOW (Reuters) - The Russian Foreign Ministry on Wednesday demanded London prove British spies did not poison a former double agent in England, saying in the absence of such proof it would regard the incident as an attempt on the lives of Russian citizens.

Ties between London and Moscow are badly strained by the poisoning of former Russian spy Sergei Skripal and his daughter Yulia in Salisbury. Britain alleges Russia was to blame, but Moscow says it had no involvement.

“An analysis of all the circumstances ... leads us to think of the possible involvement in it (the poisoning) of the British intelligence services,” the foreign ministry said in a statement.

“If convincing evidence to the contrary is not presented to the Russian side we will consider that we are dealing with an attempt on the lives of our citizens as a result of a massive political provocation.”