Lithuanian President Dalia Grybauskaite, Estonian President Kersti Kaljulaid and Latvian President Raimonds Vejonis are visiting the White House as Washington is apparently adopting a harder stance towards Moscow.

Trump's more confrontational rhetoric of late has eased initial concerns in the region over what had appeared to be a more conciliatory approach to the Kremlin when the US leader first arrived in power.

A senior Lithuanian official who wished to remain unnamed said the three Baltic leaders were asking the US to send Patriot long-range anti-aircraft missiles more frequently for war games. They also want to become a part of NATO's larger European anti-missile shield.

"I hope that the United States and other allies understand that the airspace of the Baltic states must be better protected and defended," Lithuania's Grybauskaite told her country's public broadcaster LRT ahead of the visit.

"It is important that (US troops) are here on permanent rotational basis in all Baltic states," she said.

Last year, NATO deployed four multinational battalions to Poland and the Baltic states as tripwires against possible Russian adventurism, while the US military sent a Patriot battery to Lithuania for drills.

US Vice President Mike Pence in July raised the possibility of deploying Patriots in nearby Estonia.

- Hardening line -

The Baltic states were deeply rattled by Trump's campaign rhetoric questioning NATO's relevance, his erratic behaviour and his initial unwillingness to criticise Russian President Vladimir Putin.

In 2016, Vilnius artists painted a mural depicting Trump passionately locking lips with Putin, while a public opinion poll last year showed two thirds of Lithuanians did not trust the US president.

But the public mood changed after Trump decided to provide anti-tank missiles to Ukraine to defend against Russia-backed separatists and to boost funding for US forces in Europe.

"Concerns about his commitment to NATO were initially widespread, but have eased in recent months," Vilnius University analyst Kestutis Girnius told AFP.

For Simas Celutka from the Vilnius Institute for Policy Analysis, the recent expulsion of 60 Russian diplomats in solidarity with Britain over the poisoning of a spy was a sign of a more confrontational posture.

"Advisers might have convinced Trump that a resolute show of strength is the only form of communication Putin takes seriously," he said.

- Setting standards -

Trump, who has repeatedly attacked "free rider" NATO allies, is expected to praise the Baltic trio for meeting NATO's rule to spend two percent of gross domestic product on defence.

"The president wants to show that these countries are setting standards where we want to see allies moving in terms of defence," said Anne Hall, the US ambassador to Lithuania.

The Baltic-US summit will also include a business forum where Lithuania plans to sign deals to boost imports of liquefied natural gas (LNG) from the US to reduce reliance on Russia's Gazprom.

Diplomats say the prospect of trade wars between Europe and the United States could also be discussed in the talks, as the Baltic states are increasingly concerned over a trans-Atlantic rift.

The Baltic states, with a combined population of just six million people, were occupied and annexed by Moscow during World War II.

The trio broke free from the crumbling Soviet Union in 1991 and joined both the European Union and NATO in 2004.

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