In the crosshairs of anti-whaling nations, Japan defended its annual Southern Ocean whale hunt, insisting it was gathering scientific data even as detractors accused it Thursday of harvesting meat under false pretences.

Japan denied claims at the 66th meeting of the International Whaling Commission (IWC) that it was abusing an exemption to a 30-year-old whaling moratorium which allows kills for science.

And it insisted its actions were in keeping with a 2014 ruling of the International Court of Justice (ICJ), which found that permits issued by Japan were "not for purposes of scientific research" and instructed the country to halt its JARPA II programme.

"Reports oftentimes say (that) irrespective of the ICJ judgment Japan started the research, or in violation of the ICJ judgment... and that's not true," Japan's commissioner to the IWC, Joji Morishita told fellow delegates on Thursday.

In the judgment of the court itself, "it is clear that the ICJ assumes there can be future research activities," he insisted.

"The ICJ also said... that the use of lethal sampling per se is not unreasonable in relation to the research objectives."

After the court ruling, Japan cancelled its 2014-15 hunt, only to resume it the following year under a new programme called NEWREP-A (New Scientific Whale Research Program in the Antarctic Ocean).

It killed 333 minke whales in the Southern Ocean -- many of them pregnant, according to observers.

The Southern Ocean hosts one of two whale sanctuaries in the world.

The issue is a deeply divisive and recurring one at the biennial meetings of the IWC, the world's whaling watchdog which turned 70 this year.

The meat from Japan's hunts ends up on supermarket shelves and in restaurants, in line with an IWC stipulation that whales taken for research must be eaten.

Under an IWC moratorium that entered into force in 1986, all whaling other than for aboriginal subsistence, or science, is prohibited.

- 'Deep disappointment' -

Japan hunts under the science exemption, while Norway and Iceland lodged formal objections to the moratorium and continue commercial hunts.

On the table of this year's IWC meeting is a proposal by New Zealand and Australia for a much more stringent review of scientific whaling programmes.

New Zealand's commissioner Amy Laurenson expressed her country's "deep disappointment" with Japan's resumption of whaling without IWC approval.

Japan had referred NEWREP-A to the IWC's scientific committee, but started whaling before it could complete a review, she said, and accused Tokyo of sidelining the commission.

"On the basis of the information the commission has before it, it is clear that NEWREP-A is not in fact for purposes of scientific research," the commissioner argued, and called on Japan to "cease the lethal component of NEWREP-A".

"Japan has still not justified the use of lethal sampling," she said.

Morishita insisted his country had responded to the court's concerns "in a satisfactory manner".

"We know this is a contentious issue, but facts, law and science should be the basis for further discussion on this issue," he said.

Country negotiators have been grappling with the proposal for stricter review since Monday, trying to draft a consensus text. If they fail, the proposal will be put to a vote -- possibly later on Thursday.