The surprise visit by the director of the Central Intelligence Agency to Moscow this week was to deliver a warning to Russia not to attack NATO countries, according to people briefed on the visit.

The trip was spy-agency chief John Ratcliffe’s first publicly known visit to the Russian capital, report Lara Seligman, Alexander Ward, and Josh Dawsey in the WSJ.. It followed new U.S. intelligence assessments, reported earlier by The Wall Street Journal, that Russian President Vladimir Putin could try to test the resolve of the North Atlantic Treaty Organization with a limited assault on an allied country in the next few years.

U.S. officials are concerned that Putin, squeezed in Ukraine and under pressure at home, could launch an assault ranging from a cyberattack to a small-scale land incursion, likely on a Baltic nation.

AP: Details of Tuesday’s discussions have not been revealed but such meetings normally take place only when there is a matter of pressing national security and when it is in “American national interests,” said Andrei Soldatov, an expert on Russia’s security services.