Russia sought to dismiss a report identifying one of the suspects in the attempted murder of a former Russian spy and his daughter in the British town of Salisbury as a highly decorated special service operative.

On Wednesday, two investigative online news organizations reported that one of the men who allegedly smeared poison onto the door handle of defected Russian spy Sergei Skripal was Col. Anatoliy Chepiga, a high-ranking member of the Russian military intelligence service, also known as the GRU.

Russian...