"The Chinese have been helpful in those discussions," White House spokesman Robert Gibbs said, when asked whether Beijing would clear the way for punitive sanctions against Pyongyang.

"Their reactions and reaction to the events of the past few days has been very helpful," Gibbs said.

China is viewed as an especially key player in the showdown with the Stalinist state due to its energy links with Pyongyang and supposed leverage over its reclusive neighbor.

The United States and fellow UN Security Council members were Thursday studying possible sanctions against North Korea over the nuclear test.

In April, the Security Council issued a statement of condemnation after a previous rocket launch by Pyongyang.

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