Speaking to reporters in Vilnius late yesterday, two defence officials said the United States is moving enhanced air defence assets into the region as part of multinational air drills.
The move comes amid heightened tensions with Russia, which is itself holding massive military exercises in Belarus and Kaliningrad in September.
The so-called "Zapad" drills will see Russia showcase new hardware and upgrade existing systems in its western military region, the officials said.
Pentagon chief Jim Mattis was in Lithuania today to visit a German NATO battle group and Dutch and Belgian soldiers at a training ground outside Vilnius.
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At a brief press conference with Lithuanian President Dalia Grybauskaite, Mattis refused to discuss whether Vilnius had requested a permanent Patriot missile deployment.
"We will make those decisions in consultation with the Lithuania government," he said.
"Everyone knows this is not an offensive capability."
The Patriot is a mobile air defence system made by Raytheon designed to intercept tactical ballistic missiles, low-flying cruise missiles and aircraft.
The highly militarised Russian exclave of Kaliningrad is right next door and Putin is prone to sabre rattling there.
A US-led NATO battalion that is stationed nearby in Poland and the German-led battalion that Mattis will visit are the first line of defence for the so-called "Suwalki Gap".
NATO experts see the vulnerable stretch of territory as key to eastern flank security.
The battalions will hold exercises focused on defending the Gap June 10-24.