SEOUL - The United States is open to diplomacy with the Democratic People's Republic of Korea's (DPRK) new leaders but they must improve frosty ties with Seoul and show seriousness about nuclear disarmament, a senior US diplomat said on Wednesday.

Kurt Campbell, the US assistant secretary of state for East Asia and the Pacific, arrived in Seoul on Tuesday for a two-day visit involving attendance at a forum organized by the Korea Society.

"We are open to diplomacy with the DPRK, but there is a very clear set of steps that we think are necessary," the diplomat said after meeting with Lim Sung-nam, the Republic of Korea's (ROK) top envoy to stalled talks over ending Pyongyang's nuclear program, and Vice-Foreign Minister Kim Jae-shin.

"We agreed the path is open to the DPRK toward the resumption of talks and improved relations with the United States and the ROK," Campbell said. "(But) the road to improve these relations runs through Seoul for the DPRK."

His remarks came as the ROK steps up calls for dialogue with the DPRK, an attempt to mend cross-border ties that reached their lowest ebb in 2010 following two deadly border conflicts.

The US and its allies Japan and the ROK "are still waiting to see whether the new government in the DPRK is prepared to take the necessary steps", Campbell told reporters.

DPRK leader Kim Jong-un (center) visits Unit 1017 of the People's Army Air Force in an undisclosed location in this undated recent picture released by the DPRK's KCNA in Pyongyang on Tuesday. KCNA / Reuters