US President Barack Obama has vowed to "ratchet up the pressure" on Iran over its controversial nuclear programme.
Mr Obama told CBS television Iran was becoming increasingly isolated and the US wanted to enlist the help of "a unified international community".
Amid talk of new sanctions, he earlier telephoned Chinese President Hu Jintao to seek China's co-operation.
Their talks came as Iran's top nuclear official, Saeed Jalili, said in China sanctions were "not effective".
In an hour-long phone call with Mr Hu, Mr Obama had stressed "the importance of working together to ensure that Iran lives up to its... obligations".
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