Updated

SEOUL, South Korea (AP) — South Korea demanded Monday that North Korea release a seven-man crew and their fishing boat that the country seized off the east coast days after it threatened to retaliate against the South's massive naval drills.

North Korean authorities seized four South Korean and three Chinese fishermen aboard the 41-ton South Korean fishing boat Sunday for an alleged violation of the North's exclusive economic zone. The fishermen were questioned at sea before being taken toward the North's eastern port of Songjin, according to South Korea's coast guard.

The seizure came as relations between the rival Koreas are at their lowest point in recent years following the March sinking of a South Korean warship blamed on North Korea. Tension deepened last week when South Korea launched large-scale naval training in response to the sinking, prompting its communist neighbor to warn it would counter the maneuvers with a "strong physical retaliation."

South Korea on Monday renewed its calls for a swift return of the fishermen, saying it was trying to check if their boat indeed infringed upon the North's exclusive economic zone.

Unification Ministry spokesman Chun Hae-sung told reporters that North Korea had yet to send South Korea any information on the fishermen.

"The government yesterday urged North Korea to take swift action (on the fishermen) in line with an international law and practice and I'm reiterating that," he said.

China — the North's main benefactor and traditional ally — has yet to make any response to the seizure, according to South Korea's Foreign Ministry.

Last year, North Korea freed four South Korean fishermen after detaining them for a month for illegally entering North Korean waters. The North has also been holding an American man since January for entering the country illegally and an unspecified "hostile act."

The South Korean naval drills, which were in their final day Monday, followed large-scale joint military exercises with the U.S. last month off the east coast. They included exercises near the disputed inter-Korean sea border where the warship Cheonan exploded and sank, killing 46 sailors. The area is also where the navies of the rival Koreas fought three bloody gunbattles since 1999.

The two Koreas are still technically at war because their 1950-53 Korean War ended with an armistice, not a peace treaty. The U.S. stations 28,500 troops in South Korea to deter any potential aggression from North Korea.

Military officers from North Korea and the American-led U.N. Command are to meet Tuesday at the border village of Panmunjom to discuss the sinking, the fourth such gathering since July, according to the U.N. Command that oversee the cease-fire. Previous meetings — which mainly focused on arraigning higher-level talks between the sides over the issue — ended with no major breakthrough.