Calling it a global "moment of testing," U.S. President Barack Obama appealed to Europeans on Wednesday to retrench behind the war-won ideals of freedom and human dignity, declaring that people voicing those values will ultimately triumph in Ukraine.

Painting a historical arc across the major global clashes of the last century and beyond, Obama said young people born today come into a world more devoid of conflict and replete with freedom than at any time in history — even if that providence isn't fully appreciated. He urged the 28-nation NATO alliance to make good on their commitments to the collective security that has fostered prosperity in the decades since the Cold War concluded.

"We must never forget that we are heirs to a struggle for freedom," Obama said, adding that the Ukraine crisis has neither easy answers nor a military solution. "But at this moment, we must meet the challenge to our ideals, to our very international order, with strength and conviction." 

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U.S. President Barack Obama, here shaking hands with Belgium's King Philippe while Belgian Prime Minister Elio Di Rupo looks on, called on Europe and Russia to commit to peace. Obama made the remarks during a special speech at the WWI Flanders Field Cemetery in Waregem, Belgium on Wednesday. (Saul Loeb/AFP/Getty)

Drawing on modern struggles, like gay rights, as well as the ethnic cleansing and world wars of a bygone era, Obama sought to draw a connection between the U.S. experiment in democracy and the blood spilled by Europeans seeking to solidify their own right to self-determination.

"I come here today to say we must never take for granted the progress than has been won here in Europe and advanced around the world," Obama said.

Indeed, the Europe that Obama confronted on Wednesday was taking little for granted.

Calm on the continent has been upended by Russian President Vladimir Putin's foray into the Ukrainian region of Crimea. Defying the global community, Moscow annexed that peninsula this month, stoking fears among Russia's other neighbours as Europe was plunged back into an East-West mentality that many had thought was left behind at the end of the last century.

"If the Russian leadership stays on its current course, together we will ensure that this isolation deepens," Obama said. At the same time, he acknowledged that military force would not dislodge Russia from Crimea or prevent further encroachment, holding out the allies' combination of pressure and an open door to diplomacy as the path to peace.

Obama's remarks came midway through a weeklong trip to Europe and Saudi Arabia that has been dominated by efforts to coordinate the European and American response to Putin and his government's actions in Ukraine. Earlier Wednesday, Obama pledged to defend U.S. allies during a meeting with the head of NATO, and on Monday he held an emergency meeting with leaders of major economies focused on tightening sanctions against Moscow.

Obama warned against yielding to isolationism or avoiding direct engagement in far-off crises. After all, America's economy and borders aren't deeply threatened by Russia's incursion into Ukraine and annexation of Crimea, Obama noted.

"If we defined our interests narrowly, if we applied a cold-hearted calculus, we might decide to look the other way," Obama said. "But that kind of casual indifference would ignore the lessons that were written in this continent."

Russia says Ukraine antagonizing its airline crews

Meanwhile, Russia has accused Ukrainian officials of barring Russian commercial airline crews from going outside their planes in Ukrainian airports. Ukraine denied the allegation.

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Russia claims crews on its state-controlled Aeroflot airlines are being forced to remain on board during stops in Ukraine. (Adrian Dennis/AFP/Getty)

Russia's foreign ministry said in a statement that Ukrainian border guards have been forcing cabin crews of Aeroflot, the state-controlled Russian airline, to stay inside their planes. The ministry said the decision violates international law and ultimately "poses a threat to the safety of civil aviation" because the crews cannot rest properly.

Oleg Slobodian, spokesman for the Ukrainian border service, denied any policy to keep Aeroflot crews on their planes. The only time a crew member was prevented from entry was on March 24, he said, when a passport check revealed that the man had a travel ban. In solidarity, the remainder of the crew remained on board with him.

Tensions have been high between Moscow and Kyiv since Russia annexed Crimea.

Russian authorities had previously complained that Ukrainian border guards singled out Russian men at the frontier and blocked their crossing, fearing that they may be activists coming to stir up unrest.

Paris-bound jet diverted due to Russian drills

Air France says a plane carrying 495 passengers and 22 crew was diverted on its way from Shanghai to Paris after Russia announced at short notice that part of its airspace was closed for a military exercise.

The company said flight AF111 was forced to land in Hamburg, Germany, early Wednesday to refuel because the plane had too little fuel on board to complete the flight following its detour.

Hamburg Airport confirmed that the plane landed shortly after 6 a.m. local time and was able to take off for Paris again after an hour and a half.

It wasn't immediately clear if Russia's military exercise was linked to the increased troop activity on its western border with Ukraine.

With files from Reuters and CBC News