Prime Minister Shinzo Abe claimed Thursday his push to beef up Japan's military in the face of public and parliamentary opposition would be vindicated by history.

Abe, who is being assailed for security bills that opponents say will drag Tokyo into American wars, invoked his grandfather, former premier Nobusuke Kishi -- who was arrested, but never charged, for war crimes -- as a man who had been proved right by the passage of time.

"At the time of the renewal of the Japan-US security treaty in 1960, there was strong opposition and even criticism inside the party," Abe said.

"My grandfather said that in 50 years his move would be understood, but only 25 to 30 years later a majority of the public supported the renewal of the Japan-US security treaty," he said.

As it was with Kishi, so would it be with him, the prime minister hinted.

"As to the revisions (to security legislation) this time, the situation in the world, especially in Asia, is changing, with North Korea having hundreds of ballistic missiles while developing nuclear warheads.

"To protect Japan, it is necessary to strengthen Japan-US security ties," Abe said.

Abe, a robust nationalist, has pushed for what he calls a normalisation of Japan's military posture. He has sought to loosen restrictions that have bound the so-called Self-Defense Forces to a narrowly defensive role for decades.

But unable to muster the public support to amend the constitution imposed by the United States after World War II, Abe opted instead to re-interpret it for the purpose of his bills.

Chief among the changes is the option for it to go into battle even if there is no direct threat to Japan or its people, something successive governments have ruled out.

Washington, which for 70 years has been the guarantor of Japan's security, has welcomed the move, which to many foreign eyes seems relatively uncontroversial.

However, it has proved deeply unpopular among academics and Japan's public, who are deeply wedded to the commitment to pacifism.

Many legal experts warn the bills -- based not on amendment to the pacifist constitution but changes in interpreting it -- are unconstitutional.

At the forum in Tokyo, hosted by The Economist magazine, Abe noted the comparison with his grandfather extended only so far; Kishi resigned in return for parliament's passage of the treaty renewal.

"I'm not thinking at all of calling a snap election," he said dismissing chatter that he might be forced to go to the people in a bid to rekindle his public popularity.

"As we proceed with discussions, I think people will get to understand the bills step by step, so we will explain carefully and in plain words," he said.