The powerful sister of North Korean leader Kim Jong-un on Tuesday warned of a stepped-up action against the arrival of a U.S. aircraft carrier in South Korea, claiming the U.S. move justifies the North bolstering its nuclear forces.

The U.S. aircraft carrier USS Carl Vinson arrived at the southern port city of Busan in South Korea on Sunday as a show of force against North Korea, South Korea's navy said.

The Carl Vinson Carrier Strike Group arrived in South Korea only days after Pyongyang carried out its fourth missile test this year.