Russia’s Defense Ministry said three MiG-31 fighters with Kinzhal hypersonic missiles arrived at the Chkalovsk air base in the Baltic Sea exclave of Kaliningrad as part of “additional measures of strategic deterrence.”

The ministry said the warplanes will be put on round-the-clock alert.

A video released by the Defense Ministry showed the fighters arriving at the base but not carrying the missiles, which were apparently delivered separately.

Finland’s Defense Ministry said Thursday that two Russian MIG-31 fighter jets were suspected of having violating Finnish airspace in the Gulf of Finland off the southern town of Porvoo, west of Helsinki. The Nordic country’s Border Guard started a preliminary investigation into the incident.

The deployment of Kinzhal missiles to Kaliningrad as Russia’s campaign in Ukraine nears the sixth-month mark appeared intended to showcase the Russian military’s capability to threaten NATO assets. The region borders NATO members Poland and Lithuania.