Japanese officials have confirmed the killing of more than 300 whales over a period of 115 days in their most recent "scientific" expedition in the Antarctic region.

The move was sanctioned by Japan's Institute of Cetacean Research (ICR).

According to the statement released by the ICR, the four-vessel whaling fleet that was sent out on December 1 last year has returned to Shimonoseki in southwestern Japan on Thursday, carrying 333 minke whales.

Out of the 333, 103 were males and 230 were females. It was also announced that 207 of them are pregnant when they were harpooned.

The Maritime Executive reported that the whale-hunting expedition of Japan was done within the Ross Sea, the Australian Whale Sanctuary and the Southern Ocean Whale Sanctuary.

The Australian government described Japan's resumption of its whaling program, despite being ruled as illegal by the International Court of Justice in 2014, as "deeply disappointing."

A few months back, the Australian Federal Court ordered whalers to pay $1 million fine for illegally killing whales inside the Australian Whale Sanctuary.

However, conservation group Sea Shepherd said in a statement that the governments of Australia and New Zealand did nothing to stop the slaughter.

"This rogue act is in blatant disregard of international law and diplomacy and sets a dangerous precedent for all nations that respect the rule of law," said Captain Alex Cornelissen, the group's CEO.

Minke whales are not yet considered as endangered by the International Whale Commission (IWC), but it was put on protection in 1986 due to the appreciable decline in their estimated abundance.

Japan began its "scientific whaling" in 1987. Scientific whaling, or special permit whaling, gives permission to a certain party to kill, take and treat whales for scientific research. It has been passed a year after the IWC imposed an international whaling moratorium.

Previously, Japan admitted that the meat from the harpooned whales was sold commercially, according to a Washington Post report. Over the next 12 years, Japan intends to hunt nearly 4,000 whales as part of its research and as a way of bringing back the commercial whaling industry.