Updated

South Korea on Friday rejected North Korea's demand for an immediate return of nine people who defected by boat over the weekend, despite Pyongyang's warning that could worsen their already-tense ties.

Seoul has said the nine people who crossed the disputed western sea border in two small boats Saturday want to resettle in the South. North Korea on Thursday demanded their repatriation, warning Seoul that relations between the divided countries could worsen otherwise.

South Korea's Red Cross sent a message to the North on Friday saying "all the nine people are wishing to defect so we will handle this case in accordance with their free wills," according to Seoul's Unification Ministry.

The rejection is expected to worsen already-strained ties between the Koreas, which are still technically at war because their 1950-53 Korean War ended with an armistice, not a peace treaty.

Earlier this year, North Korea responsed angrily when four of its 31 citizens who were on a boat that drifted into southern waters refused to return home. The North said the four were held against their will.

More than 21,000 North Koreans have defected to South Korea since the Korean War largely due to political oppression and economic difficulties, according to South Korean government data.

The latest defections come as North Korea is threatening to attack South Korea to protest troops' use of photos of Pyongyang's ruling family as targets during firing drills. The threat has rekindled tension, which spiked last year due to two deadly attacks blamed on Pyongyang that killed 50 South Koreans.