Lee Eun-jae of the main opposition Liberty Korea Party, who is a member of the parliamentary intelligence committee, claimed that Pompeo sent a letter to Kang.

The foreign ministry said Kang spoke with Pompeo by phone after Pompeo's trip was called off but denied there was a letter.

US President Donald Trump canceled what would have been Pompeo's fourth trip to the North, saying there hasn't been sufficient progress in denuclearization efforts.

CNN has reported that Kim Yong-chol, North Korea's top negotiator, recently sent a letter to Pompeo and warned that denuclearization talks are "again at stake and may fall apart."

North Korea has demanded the declaration of an end to the 1950-53 Korean War. The rival Koreas technically remain at war as the war ended with an armistice, not a peace treaty.

The Trump administration, however, wants the North to submit a list of its nuclear arsenal first.

The South Korean lawmakers also said South Korea sent diesel fuel to power generators in a planned inter-Korean liaison office whose construction is in the final stages.

The leaders of the two Koreas agreed in an April summit to open a liaison office in the North's border town of Kaesong to ensure active cross-border exchanges and cooperation.

On Monday, a South Korean presidential official said that the cancellation of Pompeo's trip to Pyongyang could affect the schedule of the opening of the liaison office. (Yonhap)