North Korea warned the Soviet Union in September that it would begin developing nuclear weapons independently if Moscow and Seoul normalized relations, a Japanese daily reported Tuesday.

On Sept. 30, Moscow and Seoul agreed to set up formal diplomatic ties, ending decades of hostility.Soviet Foreign Minister Eduard Shevardnadze was told during a visit to Pyongyang from Sept. 2-3 that if Moscow set up diplomatic ties with Seoul, North Korea would develop its own nuclear arsenal, the Asahi Shimbun daily quoted Japanese officials as saying.

Shevardnadze, who went on to visit Tokyo after Pyongyang, also told the Japanese government that North Korea had threatened as well to normalize ties with Japan and recognize Tokyo's claim to four north Pacific islands controlled by the Soviet Union.

On September 28, a Japanese bipartisan delegation and North Korean leaders signed a joint declaration calling for the normalizing of relations.

Three rounds of preliminary talks on normalizing ties have since been held between the Japanese and North Korean governments. Formal two-way talks are slated for February in Pyongyang.

Japanese officials are reported to be concerned about a nuclear arms race on the Korean peninsula, divided into the communist North and the capitalist South. The two countries fought a bitter war from 1950-53 and remain in tense confrontation.