— Even as an apparent truce process took halting steps in Ukraine, President Obama said Wednesday the U.S. military would expand its profile in the Western-looking Baltic states and promised NATO backing against any possible moves by Moscow in the former republics.

Obama, who was in the Estonian capital Tallinn during a day of talks with Baltic leaders, said the Pentagon planned to seek congressional approval to station additional U.S. warplanes in Estonia as part of wider Cold War-style signals to Russia of Western resolve and unity. NATO members meeting in Wales this week are expected to fine-tune plans for a rapid-reaction force aimed in particular at confronting Russia.

The U.S. plan for Estonia is an expansion of the initative Obama announced in Warsaw this spring to increase the American military presence in Europe. “Today, I can announce that this initiative will include additional air force units and aircraft for training exercises here in the Nordic-Baltic region,” he said.

Obama’s further messages of support from NATO reinforce years of increasing outreach between the Western bloc and the three Baltic states: Estonia, Latvia and Lithuania. But the comments have added urgency following Russia’s annexation of Crimea this spring and an uprising by pro-Russian rebels in others parts of Ukraine.

“You lost your independence before. With NATO you will never lose it again,” Obama told a group of mostly students during a speech at a concert hall.

President Obama called Russia's actions "a brazen assault on the territorial integrity of Ukraine" during a speech at the Nordea Concert Hall in Tallinn, Estonia, on Wednesday. (WhiteHouse.gov)

Obama also reached out to nations bordering Russia, such as Finland and others in Eastern Europe, noting that NATO membership “will remain open” to others not in the 28-nation bloc

His comments had special resonance in the Baltic region, where tensions linger between Russian-speaking minorities more than a generation after the collapse of the Soviet Union.

“As we gather here today, however, this vision is threatened by Russia’s aggression against Ukraine,” Obama said in his speech. “Reaching back to the days of the czars — trying to reclaim lands ‘lost’ in the 19th century — is not the way to secure Russia’s greatness. It only shows that unrestrained nationalism is the last refuge for those who cannot deliver real progress and opportunity to their own people at home.”

Obama’s remarks and meetings often touched on NATO’s collective defense doctrine known as Article 5.

“We have a solemn duty to each other,” he said. “Article 5 is crystal clear -- an attack on one is an attack on all. And so if, in such a moment, you ever ask again, ‘Who will come to help?’ You will know the answer: the NATO Alliance, including the armed forces of the United States of America.’’

Obama called the situation in Ukraine a “moment of testing” that “evoke dark tactics from Europe’s past that ought to be consigned to history.”

“Our NATO alliance is not aimed ‘against’ any other nation. We’re an alliance of democracies dedicated to out own collective defense,” he said. “Countries like Estonia, Latvia and Lithuania are not post-Soviet territory. You are sovereign and independent nations with the right to make your own decisions.”

Lithuanian President Dalia Grybauskaite said that Russian aggression is more than an attack against Ukraine - it’s an attack against a peaceful Europe.

“Ukraine today is a front line for all of us, and we need to take this very seriously,” she said.