Lithuania’s president said Monday Russia has deployed additional nuclear-capable missiles in its Baltic Sea exclave of Kaliningrad on a permanent basis, calling it a threat to Europe.

President Dalia Grybauskaite told reporters after visiting NATO troops in the central Lithuanian town of Rukla that “Iskander missiles are being stationed in Kaliningrad for permanent presence as we speak.” She called it a threat not only to Lithuania but to “half of all European countries.”

NATO Deputy Secretary General Rose Gottemoeller, who also visited the Rukla base where the military alliance’s multinational battalion is stationed, said Grybauskaite’s assertion, if true, was “a very serious matter,” according to the Baltic news agency BNS.

From Kaliningrad, which is sandwiched between Lithuania and Poland, Iskander missiles can reach targets in both countries as well as Baltic neighbors Latvia and Estonia, all of them NATO members.

The head of the Russian parliament’s defense committee, Vladimir Shamanov, confirmed the missiles’ deployment in remarks carried by Russian news agencies. He added that the move was a response to a NATO buildup near Russia’s borders, with the number of U.S. weapons in Poland a particular irritation to Moscow.

The high-precision Iskander missiles deployed in Kaliningrad can be fitted with a conventional or a nuclear warhead and have a range of up to 500 kilometers (310 miles.) In the past, Moscow deployed them to Kaliningrad temporarily for military drills.