TOKYO -- An International Whaling Commission panel said Monday that Japan's revised plan for research whaling in the Antarctic still lacks a convincing explanation of why it needs to kill the mammals.

"The current proposal does not demonstrate the need for lethal sampling" to achieve Japan's stated objectives, said the expert panel, part of the IWC's scientific committee.

Japan said the goal of its plan is to obtain highly accurate data to determine sustainable minke catch quotas and study the ecology of the Antarctic.

Japanese fisheries officials responded to the panel's comments by saying they are open to revisions, but did not indicate to what extent.

Joji Morishita, Japan's commissioner to the IWC, said it would be best if Japan can convince the full scientific committee by providing additional data sought by the panel's report, but cautioned that it may not be easy. The full scientific committee is to meet in May.

"The scientific committee is more political than the panel," he said. "I won't be surprised if we face some countries that oppose our plans not because of science," Morishita said. "But we hope to work toward a resumption (of research whaling) at the end of the year."

Commercial whaling was banned by the whaling commission in 1986, but Japan has continued to kill whales under an exemption for scientific research. However, the International Court of Justice ruled last year that the hunts were not truly scientific.

Following the ruling, Japan submitted a revised plan last November for the upcoming Antarctic whaling season. It said it plans to catch 333 minke whales each year between 2015 and 2027, down from a 2005-2013 annual target of up to 1,035 whales -- 935 minke and 100 fin and humpback whales. A nonlethal expedition for the 2014 season recently returned from the Antarctic.

Japan's actual catch has fallen in recent years in part because of declining domestic demand for whale meat. Protests by the anti-whaling group Sea Shepherd also contributed to the lower catch. The government has spent large amounts of tax money to sustain whaling operations.