TOKYO: Japan will strike any North Korean ballistic missile that threatens to hit Japan in the coming weeks after Pyongyang recently fired medium-range missiles, a government source said on Saturday.

Defence Minister Itsunori Onodera issued the order, which took effect on Thursday and runs through April 25, the day that marks the founding of North Korea's army, the source told Reuters on condition of anonymity.

Following the order, meant “to prepare for any additional missile launches,” a destroyer was dispatched to the Sea of Japan and will fire if North Korea launches a missile that Tokyo deems in danger of striking or falling on Japanese territory, the source said.

Tensions have been building between North Korea and its neighbours since Pyongyang - in an apparent show of defiance - fired two Rodong missiles on March 26, just as the leaders of Japan, South Korea and the United States were sitting down to discuss containing the North Korean nuclear threat.

US defence chief in Tokyo

US Defence Secretary Chuck Hagel moved on Saturday to reassure Japan of America's commitment to its security, as Russia's annexation of Crimea raises eyebrows in a region facing its own territorial disputes with an increasingly assertive China.

The United States and its allies have made clear they have no military plans to defend Ukraine, which is not a Nato member, instead moving to isolate Russia diplomatically and impose limited sanctions.

Critics say such moves are too weak to return Crimea to Ukrainian control and do little to deter further aggression.

Hagel defended the US strategy to punish Russia and told reporters ahead of two days of talks with Japanese leaders that it was natural that “allies are going to look at each other to be assured”, given the crisis in Ukraine.

“It's a pretty predictable, I think, reaction not just of nations of this area, of this region, but all over the world. It has to concern nations,” he said.

But Hagel rejected any suggestion of weakness as he renewed US commitments to Japan, which is locked in a dispute with China over islands in the East China Sea.

Washington takes no position on the sovereignty of the islands, called the Senkaku by Japan and the Diaoyu by China, but recognizes that Japan administers them and says they fall under the US-Japan Security Treaty, which obligates America to come to Japan's defence.

Addressing US and Japanese forces at Yokota Air Base, Hagel said one of the goals of his trip to the region was to assure allies of America's commitment to “our treaty obligations.” “We're serious about that,” he said. —Reuters