The North Korean Ministry of Defense said on Tuesday that the United States is again a serious threat to security by sending a nuclear submarine to a South Korean port and its military forces are ready to take any necessary action, the agency reported.

The appearance of an American nuclear submarine on the Korean peninsula is a ‘Clear expression of US unchanged hysteria for confrontation’ against North Korea, a North Korean ministry spokesman said in a statement.

“We are very concerned about the dangerous hostile US military act that can lead the acute military conflict in the area around the Korean Peninsula in a real conflict of armed forces.”said the statement reported by the KCNA news agency.

Her armed forces will “Exercise without hesitation the legal right to punish those who cause them”he said.

The South Korean Ministry of Defense said the USS ALEXANDRIA submarine entered the port of Busan on Monday for supplies and rest for its crew and that it would be an opportunity for the seafarers of the two countries to promote the exchange and combined defense.

The American Nuclear Submarine Rapid attack is part of the US Pacific fleet armed with Cruise Tomahawk rockets, according to the US Navy.

North Korea regularly criticizes the presence of US military media and joint exercises by the US and South Korean forces. On Sunday, he warned of ‘Undesirable consequences’ criticizing a series of exercises performed by the allies.

A spokesman for the North Ministry of Defense did not report separate fire exercises jointly carried out by South Korean and US armies in a firing area south of the militarized Korean border since last week.

The North has intensified aggressive rhetoric since Donald Trump assumed his duties last month for his second presidency, despite his comments that he will contact North Korea leader Kim Jong Un for immediate dialogue.