Washington: President Donald Trump's national security adviser said North Korea could dismantle all its nuclear weapons, threatening missiles and biological weapons "in a year" a far more aggressive schedule than the one Secretary of State Mike Pompeo outlined for Congress recently, reflecting a strain inside the administration over how to match promises with realism.

The statements by John Bolton, the national security adviser and historically a deep sceptic that North Korea will ever fully disarm, came as Pompeo prepares to make his third trip to North Korea late this week.

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Pompeo will arrive in Pyongyang with a proposed schedule for disarmament that would begin with a declaration by North Korea of all its weapons, production facilities and missiles. The declaration will be the first real test of the North's candour, amid increasing concern that it may be trying to conceal parts of its nuclear program.

But Bolton, appearing on CBS'"Face the Nation," said on Sunday that, nearly three weeks after the North Korean leader, Kim Jong-un, and Trump met in Singapore, no such declaration has arrived.