The security situation facing Japan is the most dangerous since the Second World War because of North Korea's "unacceptable" provocations, Prime Minister Shinzo Abe has said

The Japanese premier vowed to bolster Japan's defences in the face of the increased threat, but did not provide specific details.

Relations with the North have become more strained in recent months, particularly since the isolationist state conducted its sixth and largest nuclear test in September.

In November, the North said it had successfully tested a new intercontinental ballistic missile that could reach any part of the US mainland.

"It is not an exaggeration to say that the security environment surrounding Japan is at its severest since the Second World War. I will protect the people's lives and peaceful living in any situation," Mr Abe told a New Year news conference.

Japan increased its military budget last month for the sixth year in a row, increasing spending by 1.3 per cent to 5.19 trillion yen (£34bn).

Around 137bn yen was earmarked for improvements to ballistic-missile defences, while 11bn yen was set aside to improve warning systems to help Japan deal with more complex threats, such as multiple missiles fired simultaneously. In March, North Korea launched four missiles simultaneously that landed in the Sea of Japan.

US ambassador to the United Nations, Nikki Haley, said this week the US was hearing reports North Korea might be preparing to fire another missile, and she warned it not to.

“It is absolutely unacceptable that North Korea is trampling the strong desire of Japan and the rest of the international community for peaceful resolutions and continuing with its provocative behaviour,” Mr Abe said.

Mr Abe has said he wants to amend Japan’s pacifist constitution with the aim of loosening constraints on the military, although the public is divided over changes to the charter imposed after Japan’s World War Two defeat.

War-renouncing Article 9 of the constitution, if read literally, bans the existence of standing armed forces, but has long been interpreted to allow a military for exclusively defensive purposes.

Mr Abe said he wanted more debate on the issue.

“I would like this to be a year in which public debate over a constitutional revision will be deepened further,” he said.

North Korea announces intercontinental missile launch Show all 13 1 /13 North Korea announces intercontinental missile launch North Korea announces intercontinental missile launch Pyongyang residents react after the news of the successful launch of the new intercontinental ballistic missile AFP/Getty Images North Korea announces intercontinental missile launch North Korea's leader Kim Jong Un signing an order to test-fire the newly developed inter-continental ballistic missile KRT via AP Video North Korea announces intercontinental missile launch A news broadcast displays Kim Jong Un's signed document AP North Korea announces intercontinental missile launch People cheer as they watch the news broadcast announcing Kim Jong Un's order to test-fire the new inter-continental ballistic missile AFP/Getty Images North Korea announces intercontinental missile launch Residents react after the document signing AP North Korea announces intercontinental missile launch Pyongyang residents celebrate Kim Jong Un's announcement AFP/Getty North Korea announces intercontinental missile launch Cheering Pyongyang residents react AP North Korea announces intercontinental missile launch To counter North Korea's missile test, South Korea fired missiles into the East Sea The Defence Ministry/Yonhap via REUTERS North Korea announces intercontinental missile launch The Hyunmu-2 missiles firing during the drill South Korean Defense Ministry vi North Korea announces intercontinental missile launch The exercise was carried out in an attempt to counter Kim Jong Un's order South Korea Defense Ministry via AP North Korea announces intercontinental missile launch The South Korean army continue to carry out military exercises AP North Korea announces intercontinental missile launch Where K-9 self-propelled howitzers were taking part in a drill Rex Features North Korea announces intercontinental missile launch US soldiers are also present in the border city of Paju AFP/Getty Images

Mr Abe’s Liberal Democratic Party-led coalition retained its two-thirds “super majority” in parliament’s lower house in a 22 October election, re-energising his push to revise the constitution.