German author Boris Reitschuster claims in a new book that Russian President Vladimir Putin is forming covert, highly trained “battle groups” of sleeper agents in western countries.

In the book, due to be published this Friday, Reitschuster claims to have seen reports by a Western European intelligence service that charts the spread of such covert groups.

Joachim Ciecierski speaks to the German journalist and author on Russia, who lives in Moscow.