Lithuania wants US President Donald Trump's administration to help beef up air defence in the Baltic region as security concerns grow over Russia, President Dalia Grybauskaite said Saturday.

She also warned that measures adopted last year by NATO to reinforce its eastern flank "are no longer sufficient".

Europe has been rattled by Trump's campaign rhetoric questioning NATO's relevance, and regional security was top of the agenda as Grybauskaite and fellow Baltic presidents from Estonia and Latvia met with US Vice President Mike Pence on the sidelines of the Munich security conference Saturday.

"Without the support of the US air defence systems, we will not have full protection," Grybauskaite told AFP in a telephone interview after the talks.

"Now we are trying to purchase some of the measures ourselves but direct US participation will be necessary," she added, without elaborating on the nature of the US role she is seeking.

Lithuania, the largest and southernmost of the three Baltic states, plans to buy Norwegian NASAMS medium-range anti-aircraft missile systems in the coming years but would still lack a long-range Patriot-type system.

Poland and Romania host two US missile interceptor stations that are part of NATO's larger European shield, due to become fully operational by 2018.

US and NATO officials insist the system is intended to counter the threat of short- and medium-range ballistic missiles, particularly from so-called "rogue" states in the Middle East.

But with Poland's Redzikowo station just 250 kilometres (155 miles) from the Russian exclave of Kaliningrad, Moscow views the system as a security threat on its doorstep.

Last year Russia deployed nuclear-capable Iskander missiles into the heavily-militarised Kaliningrad, which borders both Lithuania and Poland and also holds frequent military drills in the region, rattling nearby NATO states.

The Kremlin has denied any territorial ambitions in its Soviet-era backyard and claims NATO is trying to encircle Russia.

In Munich, Pence sought on Saturday to reassure Washington's allies, saying: "Be assured that President Trump and our people are truly devoted to our transatlantic union."

Under Moscow's thumb in Soviet times, Poland and the Baltic states have been on edge since Russia annexed the Crimean peninsula from Ukraine in 2014.

At a summit in Warsaw last year, NATO agreed to deploy multi-national battalions in each of them.

But Grybauskaite said Saturday that more needs to be done to address Russian military activity and called for speedier decision-making within the US-led alliance.

"We see that Warsaw agreements are no longer sufficient. We need a faster decision-making process," Grybauskaite said, adding she expected to see progress at a NATO summit later this year.

Grybauskaite also said the US had the "full right" to push European allies to boost their defence spending to two percent of gross domestic product.

Estonia and Poland are among the few NATO nations that meet the alliance's benchmark, while Lithuania and Latvia pledged to reach it next year.