"In response to Pyongyang¹s pattern of provocative and destabilizing actions, including recent missile launches in violation of UN Security Council resolutions, I can announce today that the United States is planning to forward-deploy two additional AEGIS ballistic missile defence ships to Japan by 2017," Hagel told a joint news conference in Tokyo after talks with his Japanese counterpart, Itsunori Onodera.

The US ships would join five missile defence vessels already stationed in Japan.

North Korea last month test fired two medium-range ballistic missiles capable of hitting Japan. Tokyo has reportedly ordered its forces to destroy any North Korean ballistic missiles that pass through its airspace, and has deployed its own Aegis vessel to the Sea of Japan.

A mid-range missile fired from North Korea would be capable of reaching Japan.

The move by Washington is "driven by North Korea's continued aggressive and provocative actions and our commitment to the defence of Japan and to our treaty commitments," said a senior US defence official, who spoke on condition of anonymity.

It served "our national security interests as well," as it would contribute to missile defences, the official said, given North Korea's threats against US interests.

The US announcement followed a move in October to deploy a second early warning American radar to Japan, stationed in Kyoto, and a decision to increase the number of ground-based missile interceptors in Alaska.

"These steps will greatly enhance our ability to defend both Japan and the US homeland from North Korean ballistic missile threats," Hagel said.

North Korean leader Kim Jong-Un warned this week that the situation on the peninsula was "very grave" and vowed to "thoroughly crush" what he called a US-orchestrated policy of hostility.