U.S. defense chief James Mattis spoke with his South Korean counterpart over the telephone Monday to reaffirm Washington's commitment to defending its Asian ally, the Pentagon said in a statement, amid concerns over North Korea's nuclear program.

Mattis spoke with South Korea Defense Minister Han Min-koo amid reports that the North could conduct a test launch of an intercontinental ballistic missile (ICBM) soon.

Mattis said the U.S. commitment to defending South Korea included providing "extended deterrence using the full range of U.S. capabilities."