President Obama made a phone call to US football captain Clint Dempsey and goalkeeper Tim Howard following their elimination from the World Cup at the hands of Belgium.
A read-out of the conversation said the President had commended the players not just for their performances but for "carrying themselves in a way that made the country proud".
The statement also said the President had remarked how "captivating" the team's displays in Brazil had been.
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Mr Kim has made two recent visits to China.
The study looked at the development of 422 children over the course of eight years.
The president said they will come into force if China refuses to change its practices.