By Kiyoshi Takenaka

TOKYO (Reuters) - Japan has the right to develop the ability to make a pre-emptive strike against an imminent attack given a changing security environment although it has no plan to do so now, the defense minister said on Thursday, days after North Korea conducted a third nuclear test.

Any sign that Japan was moving to develop such a capability in response to North Korea's nuclear program could upset neighbors China and South Korea, which have reacted strongly in the past to suggestions it might do so.

"When an intention to attack Japan is evident, the threat is imminent, and there are no other options, Japan is allowed under the law to carry out strikes against enemy targets," Defence Minister Itsunori Onodera told Reuters in an interview.

"Given Japan's political environment and the peace-oriented diplomacy it has observed, this is not the time to make preparations (for building such capability).

"But we need to carefully observe the changing security environment in the region."

North Korea conducted its third nuclear test on Tuesday, drawing condemnation from the United States, Japan, Europe and the North's only major ally, China.

Onodera said Japan needed to strengthen its ballistic missile defense in view of the North Korean threat.

"Japan, the United States and South Korea managed to respond well to North Korea's missile launch on December 12. But North Korea is expected to boost various capabilities further. We need to improve corresponding capabilities as well."

But he declined to say whether it was more urgent than ever to lift a self-imposed ban on exercising the right of collective self-defense, or coming to the aid of an ally under attack.

Exercising that right is now prohibited under a long-standing interpretation of Japan's pacifist constitution but Prime Minister Shinzo Abe has made clear he wants to lift the ban and a panel of advisers has begun discussing the topic.

URGING CHINA

Onodera called on China to join the United States, Japan and other countries in tightening sanctions against North Korea, noting that Pyongyang had gone ahead with the test on Monday in defiance of Beijing's urging not to.

"I think China is the one that is most concerned about the development ... From now on, it is necessary for us, including China, to seek effective steps, effective economic measures (against North Korea)." Continued...