Japan's annual whale hunt is a commercial slaughter of marine mammals dressed up as science, Australian lawyers argued Wednesday as they urged the United Nations' highest court to ban the hunt.

Australia's case at the International Court of Justice, supported by New Zealand, is the latest step in years of attempts by governments and environmental groups to halt the Japanese whaling fleet's annual trips to harpoon minke and fin whales for what Tokyo argues is scientific research allowed under international law.

Australia calls the research claim a front for a commercial hunt that puts whale meat, considered a delicacy in Japan, on plates across the country. Commercial whaling was halted by a 1986 moratorium.

"Japan seeks to cloak its ongoing commercial whaling in the lab coat of science," Australia's agent to the court, Bill Campbell told the 16-judge panel in the wood-panelled Great Hall of Justice in The Hague.

"You don't kill 935 whales in a year to conduct scientific research. You don't even need to kill one whale to conduct scientific research," Campbell told journalists.

Japan insists its hunt is legal under a 1946 convention regulating whaling.

"Japan's research programs have been legally conducted for the purposes of scientific research, in accordance with the International Convention for the Regulation of Whaling," Japan's Deputy Minister for Foreign Affairs Koji Tsuruoka said outside the courtroom. "Australia's claim is invalid. Japan's research whaling has been conducted for scientific research in accordance with international law."

But Australia argued that the scientific whaling program, under which thousands of whales have been killed in factory ships plying Antarctic waters, was set up simply to sidestep the 1986 moratorium on commercial whaling.

"No other nation, before or since, has found the need to engage in lethal scientific research on anything like this scale," Australian Solicitor-General Justin Gleeson told the judges.

Japan's government claims the research is needed to provide data on whale populations so that the international ban on commercial hunt can be re-examined or hopefully lifted eventually based on scientific studies.

"This is something we are prepared to demonstrate: That our program is in line with Article Eight of the convention and is not commercial whaling at all," said Noriyuki Shikata, spokesman for Japan's delegation at the court.

Shikata also confirmed that Japan would be challenging the court's jurisdiction to hear the case, but did not elaborate on the reason for the challenge.

Australia is presenting its legal arguments this week and Japan will make its case starting July 2. New Zealand also gets a chance to outline its arguments July 8.

The Sea Shepherd environmentalist group, whose pursuit of Japanese whalers ensures the hunt makes news each year, said that the opening of the case was a victory for whales and vindication of the group's controversial tactics in confronting the harpooners in the icy waters of the Southern Ocean.

"Without that, trade considerations would have been more important than the slaughter of whales in Australian waters and the Antarctic whale sanctuary," said Geert Vons of the Dutch arm of Sea Shepherd, who was in court to watch proceedings.

"It's a shame it's taken 10 years, but it is good that Australia is making this public statement by bringing this case against Japan."

Campbell sought to broaden the dispute by casting Japan's decision to kill whales as undermining the global consensus to protect the broader environment.

"There is now broad recognition ... that the environment and its constituent elements are a common resource which has to be safeguarded and managed by collective action," he said.

He also highlighted the devastating effect of wide-scale whaling before it was reined in by the 1946 convention, saying that the global blue whale population was estimated at 235,000-307,000 before whaling. A 1998 estimate put the population at "a mere 2,280 worldwide," he said.

The court will take months to issue a final and binding decision on the legality of Japan's hunt.

Australian officials are hoping that the court will deliver a judgment by the end of the year, ahead of the Southern Hemisphere summer, when Japan's annual hunt begins.