South Korea criticized an adviser to Japanese Prime Minister Shinzo Abe Thursday for making an "unhelpful" visit to North Korea, voicing concerns that the trip may undermine efforts in forging a coordinated approach toward Pyongyang.

Foreign ministry spokesman Cho Tai-young made the remarks two days after the aide to Abe, Isao Iijima, arrived in Pyongyang in a surprise visit that spawned speculation that Japan may be trying to mend frosty ties with the North amid a deepening territorial dispute with China.

"It is important to maintain a close coordination, among the Republic of Korea (South Korea), the U.S. and Japan, toward North Korea," Cho told reporters.

"In that sense, we think that the visit by Iijima to North Korea is unhelpful," Cho said.

Through a "diplomatic channel" on Wednesday, Japan notified South Korea that Iijima is on a visit to North Korea and expressed "regrets" over its late notification, Cho said.

In response, South Korea delivered its stance that Iijima's visit to North Korea is "unhelpful in forging coordination with North Korea," Cho said.

However, Cho declined to comment on the purpose of Iijima's visit to North Korea or whether Japan had explained its purpose.

The North's state media reported that Iijima met with Kim Yong-il, the secretary of the North's Central Committee of the Workers' Party, on Wednesday, without giving further details.

Iijima's trip to the communist country came as the top U.S.

envoy on North Korea policy, Glyn Davies, was on a visit to South Korea on Tuesday as part of his three-nation trip that includes China and Japan.

Asked about the Japanese delegation's visit to Pyongyang, Davies replied in Seoul, "I had not heard of that, so that will obviously be something that I will discuss with the Japanese when I have a chance to talk to my counterparts there."

Japan normalized relations with South Korea in 1965, but has no formal ties with North Korea. Their relations remain frosty amid ongoing disputes over a dozen Japanese nationals the North has admitted to kidnapping decades ago.

Iijima's trip comes during heightened tension in the region over the North's nuclear and missile programs. Japan is strongly opposed to the communist country's pursuit of weapons of mass destruction.

Iijima's mission in North Korea is unclear, but he is said to have helped arrange former Japanese Prime Minister Junichiro Koizumi's trips to Pyongyang for talks with then North Korean leader Kim Jong-il in 2002 and 2004. (Yonhap News)