The younger sister of North Korean leader Kim Jong Un has issued a statement criticizing a US nuclear-powered aircraft carrier's port call to South Korea.



The USS Carl Vinson entered the southeastern port of Busan on Sunday.



Local media say the carrier is expected to take part in a joint drill among Japan, the United States and South Korea likely to be held this month.



Kim Yo Jong issued a statement through North Korea's state-run media on Tuesday saying hostile US policy toward her country offers "sufficient justification" for the North to "indefinitely bolster up its nuclear war deterrent."



She suggested North Korea will continue with its nuclear and missile development programs.



Kim Yo Jong added the North is "also planning to carefully examine the option for increasing the actions threatening the security of the enemy at the strategic level."



South Korea's defense ministry on Tuesday said the statement is "merely sophistry" to build excuses for provocations. It said any military provocation "will be met with overwhelming retaliation."



South Korea's Joint Chiefs of Staff revealed at a news conference on Tuesday that North Korean preparations for a missile launch have recently been confirmed.



The South Korean military remains on alert and is continuing surveillance.