North Korea has said it will not comply with Tokyo's demand for a resolution of the issue of Japanese citizens abducted by the North decades ago unless Japan lifts unilateral economic sanctions, sources close to bilateral ties said Thursday.

Pyongyang's demand to Japan has been made during behind-the-scene talks regarding the abductions of Japanese nationals in the 1970s and 1980s and is viewed possibly as a condition to resume investigations into the fate of the victims, the sources said.

But it remains uncertain whether Japan will heed North Korea's call, as it continues to seek a comprehensive resolution of the nuclear, missile and abduction issues.

(Sakie Yokota (R) speaks to reporters at a photo exhibition on Nov. 7, 2017, of her daughter Megumi, who was abducted by North Korean agents in 1977 at age 13)

The long-stalled issue about the missing people has seen no tangible progress since 2016 when the North disbanded a special panel to reinvestigate the victims' whereabouts in retaliation to the sanctions Japan had imposed on the North due to its continued nuclear and missile tests.

The panel was set up based on an agreement between Tokyo and Pyongyang in 2014 in Stockholm.

But during behind-the-scenes negotiations following the historic inter-Korean summit in April this year, North Korea told Japan at the working-level that the Stockholm deal has "not been scrapped," the sources said.

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It also asked for the punitive measures to be lifted, saying it disbanded the panel after Japan introduced additional sanctions in February 2016 in the wake of the North's fourth nuclear test the previous month, according to the sources.

During the working-level talks, Japan also reiterated its position that sanctions would remain in place unless the North takes concrete steps toward denuclearization, the sources said. Along with the United States, Japan has led an international pressure campaign against the North.

Japan said it is ready to normalize ties with and provide economic support to North Korea following a comprehensive resolution of the nuclear, missile and abduction issues, according to the sources.

In an attempt to achieve a breakthrough over the abduction issue, Abe seeks to hold a face-to-face meeting with Kim possibly in September on the sidelines of the Eastern Economic Forum in Russia's Far Eastern city of Vladivostok or the U.N. General Assembly in New York.

North Korea maintains the issue has been "settled," but Japan does not accept it.

Japan officially lists 17 citizens as abduction victims and suspects the North is involved in many more disappearances. Five of the 17 were repatriated in 2002, but Pyongyang maintains that eight have died and four others never entered the country.