"Incidents like this only confirm the prudence of our alliance decision last year to deploy THAAD to South Korea, and we will continue to ensure that our defense posture remains capable of deterring conflict and defending ourselves and our allies," Ross said on Monday commenting on North Korea's claim.
The commander added that North Korea's weapons programs are "a clear, grave threat" to the national security of the United States.
"North Korea openly states that its ballistic missiles are intended to deliver nuclear weapons to strike cities in the United States, the Republic of Korea, and Japan," he said.
Seoul and Washington agreed to deploy the THAAD system, designed to intercept short, medium and intermediate ballistic missiles at the terminal incoming stage, in July 2016, amid South Korea's growing unease about Pyongyang's nuclear program.
South Korea and the United States reportedly aim to complete the joint project by the end of this year, but it could be done as early as May, according to media reports.