Japan's whaling fleet in the waters off Antarctica has been attacked again by protesters, Tokyo officials have said.
Activists from the Sea Shepherd group threw containers filled with a mild form of acid made from rotten butter at a Japanese ship.
The group described it as "non-violent chemical warfare", but Tokyo condemned the actions as illegal and said several people were slightly injured.
Activists and whalers have clashed several times since last November.
The acid thrown at the whaling ship stings if it gets in people's eyes.
Officials said two crew members and two Japanese coast guard officers on one of the whaling ships complained of pain after the attack.
Japan described it as illegal and said it would lodge a protest with the Dutch authorities who license the activists' boat.
But the Sea Shepherd's Paul Watson, aboard their vessel in the Antarctic, denied anyone had been hurt.
He said bottles of butyric acid and envelopes containing "slippery powder" had been thrown at the Nisshin Maru vessel.
"We filmed and photographed the entire thing. Not a single thing landed anywhere near their crew," he told Australia's AAP news agency.
Australian Foreign Minister Stephen Smith, although a vocal opponent of Japan's whale hunt, strongly criticised the Sea Shepherd's butter attack.
"I absolutely condemn actions by crew members of any vessel that cause injury - or have the potential to cause injury - to anyone on the high seas," he said in a statement.
Japan had planned to kill up to 900 minke whales and 50 fin whales during the expedition.
Tokyo says it carries out whaling for scientific research, but critics say the same data can be collected without killing the animals.