Pyongyang, North Korea - North Korea on Friday slammed a South Korean port visit by the aircraft carrier USS Ronald Reagan, saying it showed Washington had reached "the most serious phase" of preparations for a potential nuclear war.

The nuclear-powered carrier is currently docked in the southern port city of Busan following a joint two-day maritime exercise conducted alongside ships from South Korea and Japan earlier this week.

State media outlet KCNA called the drills, which simulated the interception of North Korean smuggling vessels, an "undisguised military provocation."

They followed the most recent edition of the annual US-South Korean Ulchi Freedom exercises, which Pyongyang views as a rehearsal for invasion.

Seoul's joint chiefs of staff have announced additional drills will be conducted next week.

"The US scheme for nuclear attack on the DPRK and its implementation have reached the most serious phase of systematization and visualization," Friday's KCNA commentary said.

"It is as clear as noonday what result will be brought to the Korean peninsula, where huge armed forces and nuclear weapons are standing in confrontation with one another, even if a spark is produced," it added.

North Korea has carried out a record-breaking number of missile launches this year in defiance of international sanctions, and Pyongyang last month enshrined its status as a nuclear power in its constitution, pointing the finger at what it sees as US and South Korean provocation.