The United States and Baltic NATO allies Estonia and Lithuania signed military deals on Tuesday as President-elect Donald Trump's pro-Moscow stance stokes uncertainty about future commitments.

Fellow Baltic state Latvia has also inked a similar agreement defining the status of hundreds of US troops that are to be deployed this year to deter a more militarily aggressive Russia on NATO's vulnerable eastern flank.

These pacts also come after Washington launched a separate mission last week that will see an armoured brigade of some 3,500 soldiers and heavy equipment sent to Poland, the Baltic states and nearby NATO allies Romania, Bulgaria and Hungary.

The US-lead NATO has been increasing its military presence along Europe's borders with Russia ever since Moscow's 2014 annexation of Crimea from Ukraine.

The Kremlin denies it has any territorial ambitions and accuses NATO of trying to encircle Russia.

But Moscow's deployment of nuclear-capable Iskander missiles into its already heavily militarised Kaliningrad exclave last year and frequent military drills in the Baltic region have rattled nearby NATO states.

The defence accords, which controversially limit the jurisdiction of local courts over US military personnel, still need to be ratified by the respective national parliaments.

"It's in our interest to have US forces here, and we must have clarity over their status," Lithuanian Defence Minister Raimundas Karoblis told AFP as he concluded the so-called "status of forces" agreement with US Ambassador Anne Hall in Vilnius.

Estonia's Defence Minister Margus Tsahkna echoed the remarks, saying the accord "supports the presence of US units in Estonia and strengthens our security."

Karoblis added that Lithuania, the largest and southernmost of the three Baltic states, will host "up to 800 US troops" at a time this year.

- Trip wire -

With a combined population of six million, the three formerly Soviet-ruled Baltic nations have warily watched Trump question the US committment to guarantee the security of NATO allies.

A day after Trump declared in an interview that NATO was "obsolete", Karoblis said Lithuania was "open to discuss" his suggestion to boost the alliance's role in fighting terror.

He insisted Trump's words had "no direct link with today's agreement".

"Trump's comments and his general unpredictability have raised fears that they might encourage Russian adventurism, but there is also confidence that Trump's advisors and Lithuania's friends in Congress will ensure that support for the Baltics will not be undermined," Vilnius University analyst Kestutis Girnius told AFP.

Last year, NATO decided to deploy four multinational battalions to Poland and the Baltic states to serve as a trip wire that would automatically involve NATO allies in the event of any attack by Russia.

Some 1,200 troops will join a German-led NATO battalion in Lithuania later this year.

Over 100 Dutch personnel and four F-16 fighter are currently deployed to a NATO air policing mission guarding Baltic skies.

Lithuania has announced plans to build a fence on the border with the heavily militarised Kaliningrad, in a bid to ward off potential hybrid warfare threats which could see unmarked military personnel cross into NATO territory.

Vilnius also increased its defence budget by a third this year and pledged to meet NATO's two-percent-of-GDP funding target in 2018.