The drop-off in operations, which have involved Russian intelligence agents paying proxies to target civilian infrastructure and individuals, has been attributed to a range of factors, according to the officials, who asked not to be identified discussing sensitive issues.
A leading explanation is that Moscow may be tightening its grip on attacks entrusted to unreliable local criminals, some of which had got out of control and risked a major miscalculation, the people said.
There were 11 suspected Russia-backed hybrid incidents in Europe between January and May this year, including the attempted sabotage of fiber-optic cables and cell towers in Sweden, a report by the International Institute for Strategic Studies think tank concluded.