North Korea said it will release a South Korean fishing boat Friday after it was found illegally fishing in North Korean waters six days ago, state news agency KCNA said, as U.S. Defense Secretary Jim Mattis flew into Seoul for defense talks.

Tensions between North Korea and the United States have been building after a series of weapons tests by Pyongyang and bellicose verbal exchanges between U.S. President Donald Trump and North Korean leader Kim Jong Un, stoking fears that a miscalculation could lead to an armed confrontation.

The South Korean fishing boat was seized last Saturday and an investigation by the North proved the boat and crew had entered North Korean waters for fishing, the KCNA report said.