Exclusive-Russian mercenaries with spy links increasing presence in Ukraine – Western sources

FILE PHOTO: A Ukrainian national flag flies in front of the government building in central Kiev, Ukraine, March 3, 2016. REUTERS/Valentyn Ogirenko//File Photo

LONDON (Reuters) - Russian mercenaries with ties to Moscow's spies have increased their presence in Ukraine in recent weeks, stoking fears among some NATO members that Russia could try to engineer a pretext for an invasion, three senior Western security sources said.

They said their concerns had strengthened in recent weeks that a Russian incursion into Ukraine could be preceded by an information war, and cyber attacks on Ukraine's critical infrastructure such as electricity and gas networks.