"Under the grim security circumstances, a robust response posture and watertight coordination against North Korea are more important than ever," Han was quoted as saying.

The allies' ongoing annual joint military drills are making a big contribution to successfully deterring the North, he added.

The navies of South Korea, the US and Japan also launched a rare combined anti-submarine exercise on Monday, mobilizing some major warships and other assets.

The minister emphasized the importance of defense cooperation among the three countries, saying the trilateral training is a clear show of their resolve to deal resolutely with the North's threats.

The US commander assured him that Washington's "ironclad" security commitment to the defense of South Korea remains unchanged, said the ministry.

Swift said the US Pacific Fleet will keep playing a pivotal role in promoting cooperative ties between the two countries' navies, it added.

He plans to attend the Pacific Amphibious Leaders Symposium, an annual international forum largely on the Marine Corps, followed by a series of bilateral meetings with senior South Koran military officers.

The admiral will then head to Japan. (Yonhap)