North Korea refused to receive its 27 nationals South Korea planned to return on Friday after they strayed into southern waters on a fishing boat, the South's unification ministry said.
The North Koreans, part of the boat's 31-member crew, waited for hours near the border village of Panmunjom for an approval from their government to go home.
"A North Korean liaison officer at Panmunjom called at about 6 p.m. to deliver a verbal message demanding South Korea return all 31 of its nationals," a ministry official said requesting anonymity. "Accordingly, the 27 North Koreans are now returning to their hotel," he said.
Seoul will resume discussions with Pyongyang over the return of the North Koreans on Monday because of the weekend, the official added.
The refusal signals a new thorn in the already tense relations between the two countries that remain technically at war after the 1950-53 Korean War ended in a truce.
It also adds a twist to the fate of the 27 North Koreans wanting to go home after their tiny wooden boat crossed the heavily guarded Yellow Sea border on Feb. 5 amid foggy weather.
The North, in the message, demanded that all nationals be repatriated on the sea route along with their boat, according to the ministry. The North warned of an unspecified "enormous consequence" if the South refuses to accept its "just demand," the ministry said.
South Korea notified the North on Friday morning that it would return the 27 North Koreans through the jointly guarded border village of Panmunjom at 11 a.m. North Korea, however, did not open its border to the accept them.
The group of 31 North Koreans -- 11 men and 20 women -- underwent a month of questioning by South Korean authorities following their arrival here. Four of them -- two men and two women -- said during the last stage of the probe that they would like to defect to the South.
South Korea denies coercing them into defection, a claim rejected by North Korea, which said Thursday that Seoul engineered the defection to use them as "hostages" in a plot against Pyongyang.
"It is not true that some of the 31 people are staying due to our coercion," the ministry said in a statement, adding the four "have wished to stay on our side according to their free will and, therefore, are not returning."
The ministry also said the time and venue for the transfer of the fishing boat, docked in the western South Korean port city of Incheon, had yet to be fixed between the two countries.
The four North Koreans wanting to stay are the 38-year-old boat captain, a 21-year-old nurse, a 44-year-old jobless man and a 22-year-old female statistician, according to the ministry.
Defection is considered a sin punishable by death in North Korea. Despite the harsh penalty, defections from the impoverished state have risen. Since the 1950-53 Korean War ended in a truce, more than 20,000 North Koreans have arrived in South Korea, mostly via China.
The arrival of the 31 North Koreans came at a sensitive time because military officials from Seoul and Pyongyang were to hold their first dialogue since the North's deadly attack on the South Korean island of Yeonpyeong in November last year.
The talks broke down, prompting the North to vow not to hold any more military dialogue with the South. Tensions on the peninsula further heightened when the United States and South Korea began their joint annual military exercises this week, an event Pyongyang denounces as preparation to topple the communist regime.
North Koreans wishing to defect after accidentally crossing the inter-Korean sea border are not rare. Last year, seven people stayed while another seven returned, according to the ministry.
There were no children among the latest batch of North Koreans who arrived here by boat, according to South Korean officials.
They are believed to have left North Korea's western port city of Nampo, about 60 kilometers southwest of Pyongyang, according to military officials.