North Korea delivered a message on Thursday demanding that South Korea repatriate nine North Koreans who defected by sea over the weekend, warning that the South's failing to do so would worsen inter-Korean relations, Seoul officials said.

The North's move comes one day after local media, citing a government source, reported that three men, two women and four children crossed the tense western sea border on two engineless boats to seek refuge in South Korea last Saturday. The South's Unification Ministry, which takes charge of inter-Korean matters, first officially confirmed their defection Thursday.

"North Korea's Red Cross asked for an immediate repatriation of the North Korean defectors, citing media reports that they were under investigation by the South's authority," a ministry official said, asking for anonymity.

The North's message was delivered through a Red Cross communication channel around noon at the truce village of Panmunjom, according to the ministry.

"If (the South) does not immediately repatriate them, referring to their wishes for defection," the message warned, "it could further damage inter-Korean relations." The message also demanded that the boats be returned.

The North Koreans are being questioned by South Korean officials about their motives and their defection route, the official said, noting the government will handle the matter based on their interview results and wishes for defection.

The latest defection came four months after a group of 31 North Korean fishermen drifted aboard a troubled wooden vessel across the Yellow Sea.

Seoul has since repatriated 27 of the fishermen to the North while allowing the other four to remain in the South in accordance with their wishes.

However, Pyongyang claimed that South Korea kidnapped the 31 North Koreans and accused the South of forcing the four who wished to stay into defection, a charge that Seoul denies.

More than 21,000 North Koreans have defected to the South to avoid chronic hunger and political oppression since the 1950-53 Korean War ended in a cease-fire. (Yonhap News)