Japan's moves to improve ties with North Korea are triggering concerns that they would hamper the ongoing multilateral efforts to prevent Pyongyang's provocative behaviour and denuclearize the communist state.
On Thursday, both Tokyo and Pyongyang announced their agreement to set up a special panel to investigate the abduction of Japanese nationals and lift Tokyo's independent sanctions against Pyongyang when the probe opens.
The agreement came as Seoul, Washington and even Beijing joined forces to pressure the reclusive state to renounce its nuclear ambitions. Pyongyang has threatened to conduct a fourth nuclear test, which would further sophisticate its military nuclear capability.
Seoul expressed a cautious stance over the deal between Pyongyang and Tokyo, saying it would continue to watch the developments of the agreement. Tokyo notified Seoul of the agreement through a diplomatic channel shortly before the official announcement.
"From a humanitarian standpoint, our government understands Tokyo's position about the Japanese nationals abducted (by North Korea)," said Seoul's Foreign Ministry in a press release.
"But regarding the denuclearization issue, South Korea, the US and Japan share the view that the international cooperation (against a nuclearizing North Korea) should continue. In this regard, we will carefully watch the developments."
Under its anti-Pyongyang sanctions, Japan has prohibited people-to-people exchanges and financial transactions between the two countries, and barred North Korean vessels from calling at Japanese ports.
Observers say the lifting of these sanctions could weaken the international pressure on Pyongyang.
Koh Yoo-hwan, a professor at Dongguk University, said that in the short term, improvement in relations between Tokyo and Pyongyang would adversely impact the international cooperation against Pyongyang's nuclear adventurism. But he stressed the negative impact would only be limited from a longer-term perspective, should Pyongyang stick to its nuclear programme.
"Japan should also think about its relations with the US as well. Thus, it cannot manoeuvre wholly independently. For the relations between Tokyo and Pyongyang to get a greater boost, there should be an agreement on such things as the freeze on the North's nuclear programme," he said.
Analysts said that both Pyongyang and Tokyo had strategic interests in the improved bilateral ties.