Faced with Japan's unexpected move to engage North Korea this week, U.S. officials have notably emphasized the importance of staying close with regional powers in dealing with the nuclear-armed communist nation.

The U.S. has also been cautious in characterizing the ongoing trip by a top Japanese official to Pyongyang, while South Korea publicly disapproved.

"I should say (it's) impossible for me to speak to that without knowing the specifics on the purpose of the visit," State Department spokeswoman Jennifer Psaki said Thursday at a press briefing.

Glyn Davies, special representative for North Korea policy, also remained guarded.

"This mission that you are referring to is still under way, and I think we have some days to wait -- all of us -- before we know if there are any results from this mission," he told reporters in Tokyo, according to a transcript released by the State Department.

Isao Iijima, a key aide to Prime Minister Shinzo Abe, is on a trip to Pyongyang in what is seen as aimed at discussing the issue of Japanese citizens abducted in the 1970s or 1980s and more broadly normalizing bilateral ties.

He had meetings with Kim Yong-nam, North Korea's No. 2 official, Kim Yong-il, the secretary of the North's Central Committee of the Workers' Party, and Song Il-ho, an ambassador in charge of talks with Tokyo, news reports said.

The South Korean government described Japan's dispatch of the official as "unhelpful." Japan reportedly did not give prior notice to South Korea and the U.S. about it.

"It is important to maintain close coordination among the Republic of Korea (South Korea), the U.S. and Japan, toward North Korea," Cho Tai-young, spokesman for South Korea's foreign ministry, said at a press briefing. "In that sense, we think that the visit by Iijima to North Korea is unhelpful."

Pyongyang has repeatedly rejected dialogue offers from Seoul.

The U.S. government, however, would not use the word "unhelpful."

"I'm not going to address it in that way," Davies said, adding Washington first wants to know the results of Iijima's trip.

He said the U.S. takes the abduction issue "very seriously."

"I want to put an accent on the importance of staying very close bilaterally, trilaterally among the allies and then among the five parties, and frankly, more broadly internationally, on the issue of North Korea," Davies said.

(Yonhap News)