Tallinn (AFP) - US President Barack Obama arrived in Estonia aboard Air Force One early Wednesday to meet Baltic leaders and reaffirm Washington's commitment to the security of ex-Soviet NATO members.
The talks in Tallinn come ahead of the key alliance summit in Wales focused on the crisis in Ukraine.
Russia on Tuesday declared NATO a major "threat" after the Western military alliance announced plans to reinforce defences in eastern Europe because of the Kremlin's perceived stoking of war in Ukraine.
Obama's plane landed at 6:30 am (0330 GMT) in the capital of the small Baltic nation of Estonia which joined NATO in 2004.
Ahead of the visit the White House said Obama's mission in Estonia, where he will also meet the leaders of Latvia and Lithuania, is simple -- to put Russia on notice that it must not attempt the kind of intimidation and infiltration of NATO's former Soviet members that it has carried out in Ukraine, a non-NATO member.
"NATO has played a leading role and produced ample evidence to indicate that Russia has intervened in ways that grossly violate the territorial integrity of the independent nation of Ukraine," said White House spokesman Josh Earnest.
"It's not OK for large countries to flagrantly violate the territorial integrity of their smaller neighbours."
In Tallinn Obama will deliver a highly symbolic speech later Wednesday.
Senior Obama aides said the president will make clear that the United States regards its Article Five commitments on the collective self-defence of NATO members as sacrosanct, and will not tolerate any Russian moves on American allies.
To steel Obama's message ahead of its summit at the Celtic Manor resort in Wales, NATO has unveiled plans for a rapid reaction force of thousands of troops to reinforce the alliance's eastern flank.
Russia reacted angrily to the move, saying it was evidence of NATO's desire to aggravate tensions with Moscow, and vowed to reinforce its own defences as a result.
- Crucial moment in presidency -
This is Obama's first visit to a Baltic nation since arriving in the White House in 2009 and comes with some observers fearing that Europe is on the brink of a major conflict.
Analysts say the trip to Europe marks a crucial moment in Obama's presidency -- at a time when his foreign policy is under withering attack from rivals for failing to quell the territorial ambitions of both Russian President Vladimir Putin and IS jihadist radicals in Syria and Iraq.
"This is a very dramatic backdrop, where Europe’s security environment has turned upside down," said Heather Conley, of the Center for Strategic and International Studies in Washington.
"NATO had never thought nine months ago that it would be focusing on a robust collective defensive posture in northern Europe, but that's exactly where we are today."
Obama left Washington without commenting on a video purported to show the IS murder of US journalist Sotloff, following the killing last month of another American reporter, James Foley.
Nor did he speak to reporters on his arrival in Tallinn.
Estonia's Prime Minister Taavi Roivas believes Russia's intervention in Ukraine has fundamentally altered Europe's security and that the West must respond with a long-term strategy.
"This isn't just a period of bad weather, it's climate change. So our reaction has to be long-term," he told the Financial Times.
More than 100 prominent Baltic figures, including former leaders of Estonia Arnold Ruutel and Lithuania's Vytautas Landsbergis, on Monday urged "a permanent presence of allied troops" in the Baltic states in an open letter to Obama.
Their call echoes similar ones by leaders from across the region for permanent NATO or US boots on the ground, a move they hope will materialise at the Wales summit