The International Whaling Commission (IWC) has opened its annual meeting in Germany amid threats that Japan may pull out of the talks.
In an unprecedented and bitter attack, a senior Japanese delegate said the US, the UK and their anti-whaling allies were "liars".
Japan and Norway each kill 600-700 whales a year
He said Japan had almost lost patience with the organisation.
Sources say Japan will end its IWC subscriptions unless there is progress towards resuming whaling.
Many members expect the four-day meeting to be yet another ritual confrontation between the pro-whalers - Japan, Norway and Iceland - and the countries which are resolutely opposed to any resumption of the hunt.
Japan and Norway each kill 600-700 whales a year, as they are allowed to do under IWC rules, and Iceland wants to restart research whaling and probably resume a commercial killing programme soon.
But there is still a majority of IWC members - probably a fairly narrow one now - which opposes any resumption of whaling.
These countries want the moratorium on commercial whaling, in force since 1986, to stay in place.
They say there is no evidence the whales have recovered from the bloody destruction of the centuries of industrial whaling, and they regard the killing as inevitably inhumane.
If there's no progress we must use other options, including withdrawing from the commission
Masayuki Komatsu, Japanese delegation
On the eve of the meeting, Japanese delegate Masayuki Komatsu said the failure to make progress towards lifting the moratorium had "provoked an increased interest in the establishment of an alternative management organisation".
Japan believes the IWC promised to end the ban in 1990.
Mr Komatsu, a senior official in Japan's Fisheries Agency, told BBC News Online: "It is a sheer lie for the anti-whaling countries to say they want to complete the revised management scheme, the proposed plan to allow the resumption of commercial whaling.
"The liars are the UK, Australia, New Zealand, the Netherlands, Germany and the US.
"The US is the key: there are only two countries in the IWC that matter, the US and Japan.
"Have we lost patience with the commission? Yes and no. We are an Asian country, so we're very patient. But we are also very angry.
"If there's no progress we must use other options, including withdrawing from the commission - and that's something the biggest party in Japan has said it wants the government to consider.
"We might also decide to stop paying our subscriptions - and we and the US are the IWC's two biggest supporters financially.
"You may say we're just too optimistic, but maybe this year our patience will run out. I don't know when Japan has expressed its frustration before with such force."
Japanese Foreign Ministry sources have told BBC News Online their government will end its subscriptions if there is no progress here this week.
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