The report came after North Korea launched what it claimed to be a new intercontinental ballistic missile capable of striking all parts of the US

"We watch them closely," Manning said. "We'll remain vigilant along with our partners from the Republic of Korea and Japan, our alliance partners there, to make sure that we can counter any North Korean threat."

South Korea, the US and Japan kicked off a trilateral missile tracking exercise the same day in waters near the Korean Peninsula and Japan.

It is a routine operation focused on improving interoperability, Manning said.

"The intent of it is to ensure we maintain those readiness requirements to deal with any North Korean threat," he said, "and making sure, in essence, that we can communicate and employ the necessary capabilities to counter any North Korean threat."

Asked to provide details on last week's visit here by Gen. Vincent K. Brooks, commander of US Forces Korea, the spokesman described it as part of routine senior leadership meetings at the Pentagon.

The trip sparked considerable media speculation in South Korea as it took place shortly after the North's latest ICBM launch and amid heightened worries about a possible US pre-emptive strike on the regime. (Yonhap)