Choi said in an interview with the Yonhap news agency and other South Korean media outlets that she had "an impression chairman Kim was gradually changing his opinion" about holding a dialogue with Washington.
The diplomat stressed, however, that it was her personal opinion.
READ MORE: North Korea Summit Ends in No Deal, Was It a Failed Attempt or Complete Failure?
Kim and US President Donald Trump met in the Vietnamese capital of Hanoi earlier this week for their second summit on denuclearization which ended without agreement.
Following the Hanoi summit, Trump said that he decided to walk away from the meeting after the North Korean leader demanded full sanctions relief before denuclearization.
Meanwhile, North Korean Foreign Minister Ri Yong-ho said following the summit North Korea made realistic proposals, including dismantling its Yongbyon nuclear complex, in return for a partial lifting of sanctions.