Obama speaks to star-struck audience in Brussels

His speech sought to further isolate the Russian leadership and to bring Europe and the United States closer together by highlighting what the President described as shared values and principles.

Democracy, independent judiciaries, civil society, uncensored information, and free and fair elections were cited.

Russia's annexation of the Crimea is a throwback to the "old ways of doing things", said the US leader.

"Once again, we are confronted with the belief among some that bigger nations can bully smaller ones to get their ways," he said.

"This is not another Cold War we are entering into. After all, unlike the Soviet Union, Russia leads no bloc of nations, no global ideology. The United States and Nato do not seek any conflict with Russia," he added.

With references to war at the turn of the last century to the more recent atrocities in the Balkans, Obama said that young people are now living in a time of unprecedented peace and prosperity.

"But that is not because man's darkest impulses are vanished. Even here in Europe, we've seen ethnic cleansing in the Balkans that shocked the conscious," he noted.

Ukraine and Russia did not stray far from his speech.

But he did make references to the European project, which he said had been strained by the difficulties of integration and globalisation.

Compounded by a financial crisis, he noted the pressures had "stirred the rise of politics that too often targets immigrants or gays or those who seem somehow different".

Obama called upon European leaders to insist on policies that benefit the many and not just the few.

"Instead of targeting our gay and lesbian brothers and sisters we can use our laws to protect their rights, instead of defining ourselves in opposition to others we can confirm the aspirations we hold in common," he said.

Contentious issues such as the US-led snooping and bulk collection of Europeans' personal data was not mentioned.

He spoke of trade and open markets as interests that meet the needs of nations' citizens but did not reference the EU and US free trade deal negotiations.

At a press conference earlier in the day, Obama said he had no interest in signing a trade agreement that would weaken environmental standards or rollback consumer rights.

But his assurances are unlikely to appease critics, who complain the negotiations are conducted in secret and risk curtailing EU standards on health, food, labour rights and the environment.

For some in the audience, Obama's speech did not resonate.

"Putin is laughing in our faces," said Mihael Rotaru, a 29-year old entrepreneur from Bucharest.

Others such as a 24-year-old French student from the College of Europe in Bruges were inspired.

"It reminded me of how important peace is for us," she said.