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

Pompeo was speaking after talks with his South Korean opposite number Foreign Minister Kang Kyung-wha to prepare for a historic June 12 summit between US President Donald Trump and North Korean leader Kim Jong Un.

Some observers are concerned that South Korea's desire to build peaceful ties with the North may distance it over time from the US policy of seeking nuclear disarmament at any cost.

But both Kang and Pompeo insisted that they agreed on the need for the "total, complete, permanent and verifiable" denuclearization of the divided peninsula.

And Pompeo said the United States would remain on board to help develop the North's economy, which has been devastated by its own mismanagement and crippling international sanctions.

Pompeo has had two recent meetings with Kim to prepare for the summit and, last weekend, to negotiate the release of three Korean-Americans held in the North's jails.

He said he had had good conversations with Kim, who he found to be a focused and rational interlocutor.

"We had good conversations, conversations that involve deep complex problems, challenges, strategic decisions that chairman Kim has before him," Pompeo said.

The pair, he said, talked "about how it is he wishes to proceed and if he's prepared, in exchange for the assurances that we're ready to provide him, if he is prepared to fully denuclearize.

"We'll require a robust verification program, one that we would undertake with partners around the world which would achieve that outcome," he warned.

But he added: "I'm confident that we have a shared understanding of the outcome that the leaders want -- certainly President Trump and chairman Kim, but I think president Moon as well."

"I think that we have a shared vision for what we hope. I think there's a complete agreement about what the ultimate objectives are," he said.