Washington( CNN) As top national security officials continue to work behind the scenes to prepare for an audacious one-on-one meeting between President Donald Trump and Kim Jong Un, a key sticking point has emerged: where to hold the talks.

During CIA Director Mike Pompeo's secret Easter weekend visit to North Korea, Kim personally promised that denuclearization would be a topic of discussion during the meeting with Trump, two sources familiar with the meeting told CNN. Another administration official very well known the talks described Kim as “personable and well prepared” for such discussions.

But the venue for the talks remains the main sticking point, that official and several others familiar with the issues said.

S. Korea official: Kim Jong Un seemed sincere

Trump: We are talking directly to North Korea