In a joint press conference with David Cameron, Obama also urged Britain to stay in the EU.
“We must make sure the UK stays united,” Obama said, while making clear it was a decision for voters. And he stressed it was “hard to imagine the [European] project going well in the absence of Britain.”
His words came as Cameron argued the EU must change radically after the European Parliamentary elections.
“It is important we have people running the institutions of Europe who understand need for reform,” Cameron said, explaining why he opposed Jean-Claude Juncker being appointed as Commission President.
“It is about making some significant changes and then putting that decision in a referendum to the British people, but very much recommending that we stay in a reformed EU,” he said.
Meanwhile, Obama said he would not act on French demands that he step in and reduce a US fine of up to $10bn (£5.9bn) being faced by BNP Paribas, arguing he must stay out of the legal process.