US President Barack Obama urged young people not to "pull back" from the world and to reject cynicism and xenophobia during a Q&A in London.
Obama's comments came after he faced criticism from leading Brexit campaigners, who branded him an irrelevant "lame duck", over a speech he made supporting the UK's membership of the EU.
Barack Obama has said he hopes his pro-EU stance will help persuade British voters in the upcoming referendum - as he warned a US-UK trade deal could take up to a decade to negotiate.
Speaking to the BBC at the end of his trip to London, the US President said he expected to conclude a trade deal with the European Union before leaving office in the autumn - though said it may not be ratified during that time.
But if the UK votes to leave the EU, he added, it could take between five and 10 years to reach the same point.
The US leader has made a number of statements during his visit, voicing his view that Britain would be better off remaining a member of the EU.
"My hope is, is that this is something that would have some influence on how voters think," he said.
"For ordinary voters I thought it would be relevant to hear what the president of the United States, who loves the British people and cares deeply about this relationship, has to say about it."
Barack Obama has warned that Britain's influence on the global stage would be diminished if it votes to leave the EU.
The presidential hopeful says she agrees with Obama comments adding that she 'has always valued a strong UK in a strong EU'.
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