TOKYO (AFP) -- Japan defended its whaling as within international rules as confrontation grew in the Antarctic Ocean between Japanese whalers and environmentalists.

"I understand that Japan's research whaling follows international rules and is done for the purpose of research on whales' ecosystem," Chief Cabinet Secretary Shinzo Abe, the government spokesman, told reporters.

Abe declined to comment directly on the latest protest in which Greenpeace said one of its activists was thrown overboard into the icy ocean. Abe said he did not know the details of the incident.

Greenpeace said its activists in an inflatable boat stopped the Japanese ship from killing a minke whale for more than an hour Saturday, but that the hunters then fired a harpoon within a meter (yard) of the raft.

The harpoon killed the minke whale and its tow rope threw into the water Greenpeace activist Joe Constantine, who was able to climb back aboard the boat to safety, the environmental watchdog said.

It was the latest in a string of incidents since Greenpeace boats began shadowing a Japanese whaling fleet late last month in a bid to halt the killing of whales in the Antarctic Ocean.

Australia's Environment Minister Ian Campbell urged Monday both sides to show restraint and avoid the loss of human life in the escalating struggle.

The International Whaling Commission imposed a moratorium on commercial whaling in 1986, with countries usually allied with Japan arguing that whaling is cruel and threatens the giant animals with extinction. Japan has continued hunting despite the moratorium, using a loophole that allows killing the whales for "research."

Japan, however, makes no secret that the meat from the hunt winds up on dinner plates.