North Korea has yet to respond to South Korea's request for a joint investigation into the shooting death of a South Korean fisheries official perpetrated by North Korean troops in the West Sea last month.

In a regular briefing, Unification Ministry spokesperson Yoh Sang-key said that Seoul hopes for a swift response from Pyongyang.

South Korea's presidential office last week requested a joint probe with North Korea to get to the bottom of the fatal incident, noting discrepancies in the assessment of the event between the two Koreas.

Seoul has also asked the North to reopen the inter-Korean military communication line.

Meanwhile, the South Korean military and Coast Guard continue to search for the remains of the official for the 15th day, with the search area slightly expanded to the south by some 15 kilometers. 

Thirty-two vessels and six aircraft were mobilized for Monday's search in waters near the border island of Yeonpyeong.

A Coast Guard official said there is currently no set date to end the search.