"We express grave concern over the US dangerous hostile military act that can lead the acute military confrontation in the region around the Korean peninsula to an actual armed force conflict," a defence ministry spokesperson said in a statement carried by state news agency KCNA.

They warned the United States to "stop provocations stirring up the instability any longer," accusing it of ignoring North Korea's security concerns.

Yonhap news agency reported that the USS Alexandria, a nuclear-powered submarine, arrived at Busan naval base in South Korea on Monday. A similar visit was made last November.

"Our armed forces are strictly watching the frequent appearance of the US strategic means on the Korean peninsula and are ready for using any means to defend the security and interests of the state and the regional peace," the defence ministry spokesperson said.

They noted the importance of developing the North's self-defence capabilities and referenced leader Kim Jong Un's vow in January that his country's nuclear programme would continue "indefinitely."

Largely cut off from the world diplomatically and economically, and under a bevy of sanctions, North Korea's nuclear weapons programme has been a major thorn in the side of the United States for years.

President Donald Trump, who had a rare series of meetings with Kim during his first term, has said he will reach out to the North Korean leader again, calling Kim a "smart guy".

A summit between the two in Hanoi collapsed in 2019 over talks on sanctions relief and what Pyongyang would be willing to give up in return.

North Korea said earlier this month it would not tolerate any "provocation" by the United States after top US diplomat Marco Rubio called it a "rogue state" in a radio interview.