STOCKHOLM (Reuters) -Sweden will expel three Russian diplomats for spying, Foreign Minister Ann Linde said on Tuesday, joining a number of European countries which have expelled Russian diplomats in recent days. “It is because they are not following the Vienna Convention and they are undertaking illegal intelligence-gathering operations,” Linde told reporters. France, Belgium and the Netherlands have recently expelled Russian diplomats over alleged spying activity. The moves coincide with outrage across the continent over reports of the discovery of mass graves and of civilian killings in the …