South Korea's navies, the United States and Japan will begin two-day anti-submarine drills on Monday to improve capability to counter North Korea's nuclear and missile capabilities, South Korea's defense ministry said.
The drill is scheduled to take place in international waters off South Korea's South Jeju Island, involving a U.S. aircraft carrier group led by the USS Nimitz, which arrived in the southeastern city of Busan last week.
The trilateral drills come as North Korea last week unveiled new, smaller nuclear warheads, pledged to produce more weapons-grade nuclear material to bolster its arsenal and boasted of a drone capable of underwater nuclear attack.
This week's drills will use a mobile target for anti-submarine warfare training to improve capabilities needed to detect, track and destroy underwater North Korean threats, the ministry said.
The three countries held their last triple anti-submarine drills in September, the first time in five years, amid tension over an unprecedented number of North Korean missile tests.
North Korea on Sunday condemned such joint exercises, warning - according to state media in Pyongyang - that it does not say "empty words" when it comes to its nuclear capabilities, and that the United States and South Korea are engaged in "wrong behavior by exposing themselves to serious danger."
A U.S. research site reported that satellite images showed a high level of activity at North Korea's main nuclear site after the country's leader ordered increased bomb fuel production to expand the country's nuclear arsenal.
On Tuesday, Pyongyang unveiled new, smaller nuclear warheads and pledged to produce more weapons-grade nuclear material to expand its arsenal.