South Korea and the United States strongly indicated Thursday that their support for improvement in North Korea-Japan relations is conditional amid a drawn-out stalemate in efforts to denuclearize the communist nation.

Following reports of a fresh deal between Pyongyang and Tokyo over the issue of Japanese citizens abducted by North Korea decades ago, South Korean officials warned of a possible negative impact on the troubled denuclearization process.

"We understand the importance of the abduction issue in Japan's diplomacy, but now is an important time for South Korea, the U.S., Japan, China and Russia to cooperate for the denuclearization of North Korea and preventing North Korea from advancing its nuclear capability," a senior South Korean diplomat here said on background.

He was referring to Pyongyang's dialogue partners in the six-party nuclear talks.

A push for resolving the abduction matter should proceed in concert with efforts to address the nuclear problem, added the official.

His comments represent Seoul's formal position on the agreement between North Korea and Japan in high-level talks in Stockholm earlier this week.

Pyongyang agreed to reopen an investigation into the fate of Japanese nationals it abducted in the 1970s and 1980s. In return, Japan said it would lift some sanctions on Pyongyang.

Seoul is apparently concerned that Tokyo's move may send the wrong signal to Pyongyang, which refuses to take steps toward denuclearization while sticking to military threats.

The South Korean official took issue with the timing of Japan's prior notice of its plan for talks with Pyongyang.

"(We) received a notification in advance but it was just before (the announcement of the plan for talks), which provided no sufficient time (for coordination)," he said.

The U.S. government also said it was notified in advance and indirectly emphasized the need for transparency in engaging in talks with Pyongyang.

"We were alerted that they are planning to engage in those discussions," Jen Psaki, the State Department's spokeswoman, said at a press briefing. "We continue to support Japanese efforts to resolve the abduction issues in a transparent manner." (Yonhap)