US President Barack Obama has expressed hope for a reported ceasefire between Ukraine and Russia over the rebellion in eastern Ukraine during a visit to Estonia.
Obama's visit to Tallinn, the capital, appeared to be aimed at showing Washington's solidarity with the three Baltic states, one day before a NATO summit in Wales, where Russia's involvement in Ukraine is expected to be the main topic.
At a joint news conference with his Estonian counterpart Toomas Hendrik, Obama said: "Just hope it [the ceasefire] works.
"But we need to be clear and consistent in language we use to describe situation in Ukraine.
"As the EU underlines, this is Russian aggression. The EU and US are ready to take further restrictive measures in response to Russia’s behaviour."
He also said that Estonia was acting as a buffer zone against "Russian agreession" in the east, adding that the country has been a great ally, fulfilling its duties towards NATO.
Obama will also meet with the leaders of Latvia and Lithuania later on Wednesday to offer reassurances to all Baltic NATO member states located near the Russian border, following the alleged Russian-backed military offensive in Ukraine.
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The Baltic states are seen by some as especially vulnerable to Moscow's attention because of their Russian minorities and high dependence on energy shipments from their larger neighbour.
At the two-day summit in Wales, the Baltic states will press for some kind of deployment of NATO troops, in addition to increased air patrols already announced by the alliance this year.
NATO agreed this week to create a "spearhead" rapid reaction force, potentially including several thousand troops, that could be sent to a hot spot in as little as two days, down from an earlier response time of around five days.
But the military alliance remains divided on setting up permanent bases in the east.
Moscow revising defence policy
On Wednesday, a top Russian defence official said Moscow would adopt a new military doctrine over NATO's expansion and the alliance's plans to establish the rapid-response force in the wake of the rebellion in Ukraine's east.
Russian Defence Minister Sergei Shoigu said in separate comments on Tuesday that Russia's armed forces would be given added muscle with the deployment of 230 new helicopters and fighter jets by the end of the year.
Sergei Lavrov, the Russian foreign minister, said that Ukrainian moves to seek NATO membership were aimed at undermining efforts to end the war in the east of the country.
Anchored in NATO, unlike Ukraine, the three Baltic states have far less cause to fear a full-blown Russian military invasion, but they worry about cyberattacks and other more stealth-like forms of aggression.