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Top Chinese nuclear experts warned the U.S. that North Korea may already have 20 nuclear warheads and could double its arsenal by 2016, according to a report in the Wall Street Journal.

The worries were conveyed to American nuclear officials during a private meeting, the newspaper reported, citing people briefed on the matter.

The Chinese experts estimated that Pyongyang may already have 20 warheads, in addition to the capacity to make enough uranium bring that number to 40 next year, the Wall Street Journal reported. NBC News was not immediately able to confirm the report and U.S. officials were not immediately available for comment.

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American estimates reportedly put the number of North Korean bombs at between 10 and 16. The much-higher Chinese estimates suggest that North Korea could threaten the region and U.S allies, according to the newspaper. The U.S. has mutual defense treaties with South Korea which would mean that an attack on Seoul would be seen in Washington as an attack on the United States.

According to the paper, the Chinese are increasingly concerned that President Barack Obama is focusing on finalizing a nuclear deal with Iran at the expense of dealing with the nuclear threat from North Korea.

China's Foreign Ministry spokesman Hong Lei said he "did not have knowledge of the specific situation" when he was asked about the report during a regular press briefing on Thursday, according to Reuters.

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— F. Brinley Bruton

Reuters contributed to this report.