WASHINGTON-- U.S. Defense Secretary Jim Mattis assured his South Korean counterpart that any North Korean threat to the allies will be met with a "massive, effective, and overwhelming" military response, his spokesperson said Wednesday.

During a phone call Tuesday, Mattis and South Korean Defense Minister Song Young-moo discussed North Korea's sixth and most powerful nuclear test conducted over the weekend.

"Secretary Mattis assured Minister Song that the United States remains ironclad in its commitment to the defense of the ROK," Pentagon chief spokesperson Dana White said in a statement, using the acronym of South Korea's official name, the Republic of Korea. "He further emphasized that any threat to the United States, its territories, or its allies will be met with a massive, effective, and overwhelming military response."

Mattis made similar remarks following a meeting with President Donald Trump on Sunday.

The defense chiefs also discussed ways to improve bilateral, trilateral and regional defense cooperation for the peace and stability of Northeast Asia and the broader Asia-Pacific region, White said.

In an earlier statement summarizing the call, South Korea's defense ministry said Song and Mattis agreed to bolster the combined defense posture and deter North Korean provocations by strengthening the regular deployment of U.S. strategic military assets and joint military exercises on and around the Korean Peninsula.

They also agreed that the international community should fully implement current sanctions on North Korea and adopt new punitive measures, it said.

During a phone call with Japanese Defense Minister Itsunori Onodera the same day, Mattis said the U.S. would help enhance Japan's ballistic missile defense capabilities, White said in a separate statement.

The secretary also underscored the "ironclad" U.S. commitment to defend Japan, including through extended deterrence.

"Secretary Mattis and Minister Onodera confirmed their intent to continue working trilaterally with the Republic of Korea to strengthen deterrence and to maintain the peace and security of Northeast Asia," White said.

Source: Yonhap News Agency