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

Pyongyang’s demand to Japan was made during behind-the-scenes talks regarding the abductions of Japanese nationals in the 1970s and 1980s, and is viewed possibly as a condition for resuming 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 comprehensive resolution of the nuclear, missile and abduction issues.

The long-stalled probe into the missing people has seen no tangible progress since 2016, when the North disbanded a special panel to reinvestigate the victims’ whereabouts in retaliation for sanctions imposed by Japan on the North due to its continued nuclear and missile tests.

The panel had been set up based on an earlier agreement made between Tokyo and Pyongyang in 2014 in Stockholm.

But during diplomatic exchanges at a working level following the historic inter-Korean summit in April this year, North Korea told Japan that the Stockholm deal has “not been scrapped,” the sources said.

It also asked for the punitive measures to be lifted, saying it had 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, Tokyo also reiterated its position that sanctions would remain in place unless the North takes concrete steps toward denuclearization, the sources said. Together with the United States, Japan has led an international pressure campaign against the North.

Tokyo has 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 is seeking 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 that the issue of abductions of Japanese nationals has been “settled,” but Tokyo does not accept this.

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.