The U.S. is considering deploying more missile defense assets to Asia to counter North Korea’s nuclear and missile threats, said Adm. James Winnefeld, the vice chairman of the Joint Chiefs of Staff, in a speech during a security forum in Washington, D.C., on Wednesday.

Describing North Korea, along with Iran, as the “chief threats” to the U.S., Winnefeld underscored the need to deploy a Terminal High-Altitude Area Defense battery in South Korea. He said Washington was in talks with Seoul over the new deployment.

The THAAD is designed to shoot down short-, medium- and intermediate-range ballistic missiles during their terminal stage. Seoul has remained reluctant over the deployment of the THAAD system as it could be perceived as participation by Seoul’s in the U.S.-led missile defense program, which would unnerve China and Russia.

During the forum, the vice chairman stressed that a robust missile defense should remain America’s top missile defense priority.