Amid growing tensions in the Korean Peninsula, North Korea showed humanitarian gesture by saying it will release a South Korean fishing boat, state media KCNA reported Friday. "391Hungjin" and its crew were captured off the North's east coast six days ago for "illegally" sailing into its waters.

The crew confessed they had deliberately crossed the border for fishing, KCNA claimed, adding the North, however, decided to repatriate them "from the humanitarian point of view" after the crew apologized for their actions and asked for leniency. 

The South Korean government confirmed the report of North releasing their citizens. 

"We find it fortunate that our fishing ship and its crewmen are being returned," said a spokesman for Seoul's unification ministry handling North Korea affairs.

The latest incident comes amid ongoing military exercises in the region as North Korea continues to grow its nuclear arsenal and the South's deployment of a U.S.-backed missile defense system to counter Pyongyang's growing threats. 

Earlier this month, the U.S. and South Korea began joint military exercises in waters surrounding the Korean peninsula, involving fighter jets, destroyers, and aircraft carriers — a move that North Korea has termed as provocative and "rehearsal of war."

On Friday, U.S. Defence Secretary James Mattis arrived in Seoul for annual defense talks with South Korea as a part of Asia tour. During his visit, he warned Pyongyang to stop threatening "catastrophe" with its nuclear weapons.

Mattis made the brief comments alongside South Korean Defence Minister Song Young-moo, describing Kim Jong Un's leadership as an "oppressive regime" that mistreats its people while praising South Korea for its vibrant democracy.

North Korea has continued to grow its nuclear arsenal in recent months, testing ballistic missiles and issuing threats against the U.S. North Korea warned last week of an “unimaginable strike” on the U.S.

"The U.S. is running amok by introducing under our nose the targets we have set as primary ones," North Korea’s state news agency said in a statement. "The U.S. should expect that it would face unimaginable strike at an unimaginable time."