The UN special rapporteur on North Korea's human rights situation has sent the two Koreas letters calling for sufficient information on the North's killing of a South Korean fisheries official in September, a diplomatic source said Thursday.

On Tuesday, Tomas Ojea Quintana handed the "joint communication" letters to the diplomatic missions of the two Koreas in Geneva, Switzerland, as Pyongyang has yet to respond to Seoul's call for a joint probe into the official's death, with his family calling for a UN investigation.

The 47-year-old official was shot to death at sea by the North Korean military after drifting into North Korean waters, Seoul officials have said, tentatively concluding he attempted to defect to the North. His family has rejected the possibility of his defection.

The foreign ministry refused to comment on the content of the letter but said it plans to send a reply two months later as Quintana requested.

"We cannot disclose the content of the letter, but the UN special rapporteur is supposed to make public both the letter and our reply sixty days later," a ministry official said on condition of anonymity.

The defense ministry said it received the letter via the foreign ministry on Wednesday.

"Based on related law, we will respond to the UN request in close coordination with other government agencies," defense ministry spokesperson Col. Moon Hong-sik said during a regular press briefing.

In October, the Office of the UN High Commissioner for Human Rights in Seoul called on both Koreas to conduct a "prompt, impartial" probe and urged Pyongyang to engage with Seoul to facilitate the return of the remains of the deceased and his personal belongings to his family. (Yonhap)