"During my meeting with H.R. McMaster, we will check North Korea's current military threats and the possibility of its provocations, and further strengthen the robust South Korea-US alliance system," Kim said at Incheon International Airport, west of Seoul.

Calling the current security situation on the peninsula "grave," Kim also warned that Pyongyang is ready to stage yet another provocation "at any time."

In recent months, the communist state has been ratcheting up cross-border tensions with a series of missile tests.

Last Monday, the North fired off four ballistic missiles toward the East Sea apparently in an angry reaction to the ongoing military drills by Seoul and Washington, which it has denounced as a rehearsal for an invasion.

The latest provocation came less than a month after its launch of a new intermediate-range ballistic missile that underscored how it is on course towards developing a nuclear-tipped ballistic missile that threatens not only South Korea but also US bases in the Pacific rim.

According to 38 North, a North Korea-monitoring website, Pyongyang has been seen excavating a tunnel at its Punggye-ri nuclear test site in the northeast, a move that analysts say could indicate ongoing preparations for yet another nuclear experiment.

Observers say the allies' security chiefs are also expected to reaffirm their determination to install a US missile defense battery on the peninsula as planned, despite strong objections from China and some liberal opposition parties here. Beijing has strenuously opposed the deployment scheme, arguing it would hurt China's security interests. (Yonhap)