TOKYO — Japan said Tuesday it would staunchly defend its research hunt that kills hundreds of whales per year, a day after Australia filed an international lawsuit arguing that the cull does not qualify for a scientific exemption to a 1986 ban.

Australia -- Japan's major trading partner -- filed its lawsuit with the International Court of Justice in The Hague on Monday, officials in both countries confirmed, after Canberra announced its intention last week to file suit following years of fruitless diplomatic efforts to end the hunt.

Chief Cabinet Secretary Hirofumi Hirano -- Japan's top government spokesman -- called Australia's action "extremely regrettable." A Japanese Foreign Ministry official in charge of whaling said that Tokyo would defend itself before the international court.

"We cannot accept Australia's argument at all," ministry official Yutaka Aoki said. "We will firmly respond to the lawsuit."

Japan joins Norway and Iceland in hunting whales under exceptions to a 1986 moratorium by the International Whaling Commission. Japan says its hunt falls under an exemption that allows for scientific research, but opponents call Japan's scientific research whaling program a cover for commercial hunts.

Excess meat from the program is in Japan for consumption, available through limited outlets such as special whale restaurants and public school lunch programs.

Australia's case maintains that Japan's hunt is essentially for commercial purposes and that it fails to qualify for the scientific exemption, partly because of "a lack of any demonstrated relevance for the conservation and management of whale stocks," according to court documents.

New Zealand has said it will decide within weeks whether it will file a similar case against Japan.

Japanese officials say whaling is a national tradition and a vital part of the country's food culture. Tokyo also argues whale stocks have sufficiently recovered since 1986 to allow a resumption of limited hunts among certain species.

The International Whaling Commission, which will meet later this month in Morocco, is currently mulling a plan that would effectively allow commercial whaling for the first time since the ban, but under strict quotas.

Escalated confrontations between activists from the group Sea Shepherd and Japanese vessels have forced Japan's Antarctic mission in recent years to return home with only half its catch quota of some 900 whales.

Sea Shepherd activist Peter Bethune, 45, who boarded a Japanese whaling ship in Antarctic seas as part of a protest in February, pleaded guilty last week to charges including trespassing and destruction of property. If convicted, he faces up to 15 years in prison.

Bethune is the first Sea Shepherd arrested by Japan over the conservationists' aggressive campaigning against whaling. Japans' whaling program involves large-scale expeditions down to the Antarctic, while other whaling countries mostly stay along their coasts.