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 that the U.S. move highlights the North's urgency to bolstering its nuclear forces.

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

The Carl Vinson is the first U.S. carrier to visit Busan since the USS Theodore Roosevelt docked there on June 24. Days later, the Theodore Roosevelt and its strike group took part in Freedom Edge, the first major trilateral maritime and aerial exercise involving the United States, South Korea and Japan.