US Secretary of State John Kerry has told a news conference that talks on Iran are "not a race" to complete just any agreement on the country's nuclear programme.
He added that the US hopes to reach a deal with Iran "within the next months" and that he was confident the agreement would "protect Israel".
Marathon talks between the P5+1 - the United States, Russia, China, Britain, Germany and France - and Iran on Saturday did not end in an agreement. The sides arranged to meet again on Nov. 20.
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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.