The Democratic People's Republic of Korea (DPRK) demanded South Korea to repatriate nine nationals who had crossed the "inter-Korean maritime border" in waters off the west coast of the Korean Peninsula last week, Seoul's Ministry of Unification said Thursday.

The ministry said in a press release that the DPRK's Red Cross sent a message to the South earlier in the day, calling for early return of the nine nationals.

The ministry confirmed earlier media reports that nine DPRK nationals crossed the Northern Limit Line (NLL) on Saturday by boat and expressed their intention to defect to the South. They are currently being investigated by the South.

According to local media, the nine DPRK nationals, including three men, two women and four children from families of two brothers, arrived at a small islet near Yeonpyeong Island in west waters in two small boats on Saturday to seek refuge in the South. Seoul's military, police and intelligence agency are currently investigating their motives and route.

However, Seoul's Unification Minister Hyun In-taek, the country's top official in charge of inter-Korean affairs, said he was kept in the dark about the incident, noting that he first heard about it through media reports.

The incident came four months after 31 DPRK fishermen crossed the contentious sea border NLL by boat on Feb. 5. Twenty-seven of them were sent back to the DPRK in late March, while other four who officials here say wish to stay in the South remained. But Pyongyang accused Seoul of abducting the crewmen and forcing them to defect.

South Korea and the DPRK have remained at odds on the so-called NLL, which was fixed unilaterally by the U.S.-led United Nations Command after the 1950-1953 Korean War.

South Korea holds the NLL as the de-facto western inter-Korean border, but the DPRK rejected the NLL and only recognized the demarcation line it drew in 1999, which was further south of the NLL.