NATO Secretary General Jens Stoltenberg on Friday expressed concern over Russian spying activities within the Western military alliance.
"We have seen that Russian intelligence services have operated across European countries for many years. We also see attempts to step up their activities, but of course NATO allies are monitoring and following this very closely," Stoltenberg said in an interview with Germany's top-selling Bild daily.
"And we have also taken some measures to make it harder for the Russian security intelligence services to conduct illegal activities among or inside NATO allied countries," he added.
Stoltenberg said several Russian personnel had in the past been expelled from NATO headquarters amid espionage allegations.
"We also expelled for instance Russian personnel from NATO headquarters because we saw that they were conducting activities which were actually not diplomatic work but intelligence work," he said.
Russia established a diplomatic mission to NATO in 1998 which was closed after cooperation under the NATO-Russia Council was suspended in 2014.
In related news, Stoltenberg warned Europe against trying to go it alone on defense after comments by US Republican presidential contender Donald Trump prompted renewed debate over whether the continent can continue to rely on protection from the United States.
"We have NATO, and NATO is the cornerstone for European security, and NATO has been able to protect all NATO allies for 75 years," he said.
NATO is meant "to bind Europe and North America together," he added.
"So as long as we stand together we're safe," the leader of the Western military pact reiterated.
Stoltenberg also said it was still unclear when Ukraine would receive its long-awaited F-16 fighter jets.
"I will always welcome that things can go as fast as possible and the time matters on the battlefield in Ukraine. At the same time, I think we have to remember that to deliver F-16s will take some time, not mainly to prepare their planes but mainly because it is important to have trained pilots," he said.
"I know the (NATO) allies are now working hard to get this planes ready but more important is to get the pilots and the support team ready," Stoltenberg added.
