"If North Korea takes bold action to quickly denuclearise, the United States is prepared to work with North Korea to achieve prosperity on par with our South Korean friends," said Mike Pompeo.

Mr Pompeo said there would need to be "complete" and "robust verification" of denuclearisation, suggesting it would involve inspections to ensure the North's compliance.

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"We talked about the fact that America has often in history had adversaries who we are now close partners with and our hope that we could achieve the same with respect to North Korea," he said.

He made the announcement at a joint news conference with South Korean foreign minister Kang Kyung-wha.