Washington (CNN) Secretary of State Mike Pompeo heads to North Korea on Thursday under pressure to produce tangible signs of progress as US intelligence reports cast doubt on Kim Jong Un's intention to dismantle his nuclear and missile programs.

The top US diplomat has offered few details about the state of negotiations following the June summit in Singapore between Kim and President Donald Trump, but knows he must return from his third trip to North Korea in as many months with concrete plans for a path forward, sources tell CNN.

"Pompeo has already been to Pyongyang twice and -- as Singapore made clear -- came away with very little to show on the core US interest of denuclearization," according to John Hannah, senior counselor at Foundation for Defense of Democracies and former senior adviser to Bill Clinton's Secretary of State Warren Christopher.

"It should not happen a third time without Kim understanding that -- while diplomacy might continue -- there will be consequences in terms of a ratcheting up of the maximum pressure campaign, and certainly no prospect of another summit with President Trump," Hannah said about Pompeo's upcoming trip.

While Pompeo has told CNN that he is not willing to lay out a timeline for talks, he noted that he wants to see continued progress showing Kim is serious about dismantling his nuclear program and that he plans to discuss next steps when the two meet this week.

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