North Korea has told China through formal diplomatic channels that it will reject any attempt to discuss its past abductions of Japanese nationals during upcoming six-nation talks on its nuclear program, sources said Thursday.

Japan has said it wants to take up the abduction issue during the three-day talks that begin in Beijing on Wednesday. The participants are Japan, the United States, China, North Korea, South Korea and Russia.

While the North Korean media has repeatedly aired messages threatening Japan not to mention the abductions, it is the first time that any message has emerged through diplomatic routes, according to the sources, who are versed in Sino-North Korean affairs.

Some observers said that if Tokyo mentions the issue at the start of the Beijing talks, Pyongyang might walk away from the negotiation table.

The sources said North Korea told Japan earlier this month when it agreed to the six-way talks that discussion of the abduction issue "would be an obstacle." When China's Vice Foreign Minister Wang Yi visited North Korea this month to discuss the upcoming talks, North Korean officials said they "cannot accept" any effort by Japan to bring up the abduction issue, the sources said.