An Icelandic whaling company has been accused of slaughtering an endangered blue whale.

International anti-whaling activist group Sea Shepherd claims the huge animal was killed by the Hvalur hf whaling company, which is licensed by Iceland's government to slaughter smaller fin whales.

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At the time of writing, there was still conjecture over the exact identification of the whale, with some suggesting it may be a hybrid of a blue whale and fin whale, which do occur in Iceland's waters.

Photos provided by Icelandic-based anti-whaling group Hard to Port show the huge animal being towed into port and hauled ashore, with crew members seemingly posing for photos beside it before it was cut up.

One crew member can be seen posing for a photo while sitting on top of the whale.

In a statement on the Sea Shepherd website, founder Paul Watson said the slaughter had brought disrepute to Iceland.

"I know a blue whale when I see one and this whale slaughtered by [Hvalur's CEO] Kristjan Loftsson is a blue whale," he said.

"This man must be stopped from ruthlessly violating international conservation law and bringing such disrepute to the nation of Iceland.

"There can be no legal justification for this."

Speaking to Icelandic media, Gisli Arnor Vikingsson from the Iceland Marine Institute said he also believed the animal was a blue whale–fin whale hybrid.

"Photographs point to the fact that it's a hybrid whale and we're almost certain that it is one, but we can't be sure until autumn when we get it DNA tested," he said.

Hard to Port agreed the whale could be a hybrid.

Sorry, this video has expired Icelandic whalers pose for photos with blue whale carcass

Time for Iceland to give up 'cruel, inhumane practice'

According to the International Union for the Conservation of Nature (IUCN), no blue whale has been deliberately caught since 1978.

Whaling in the 1900s decimated blue whale populations by up to 90 per cent, according to the IUCN, though present numbers are difficult to calculate.

The whale meat being cut up on the side of the dock. ( Supplied: Sea Shepherd )

Although an international moratorium has placed catch limits at zero for blue whales, Iceland, Norway and the Russian Federation all objected to that provision.

Iceland resumed commercial whaling in 2006, joining Norway in open defiance of the International Whaling Commission's (IWCC) ban.

Iceland and Norway began exporting whale meat to Japan in 2008.

So far this season Hvalur hf has killed 21 fin whales, according to Sea Shepherd, which has been monitoring the catch.

Sea Shepherd say the crew took photos and posed with the whale. ( Supplied: Sea Shepherd )

But this latest incident should be a wakeup call to the people of Iceland, Humane Society International's Head of Campaigns Australia Nicola Beynon said.

"It looks like a blue whale, but if not a blue whale then it's a hybrid. They're highly endangered animals", she said.

"It is unforgiveable. We hope that the Icelandic public give their whaling group a hard time about this. The cruel and inhumane practice of commercial whaling does not belong in the 21st century, it's time to give it up."

Blue whales are the largest animals ever to have lived.

Two species of blue whale are found in Australian waters, according to Macquarie University researcher Vanessa Pirotta.

The pygmy blue whale and the Antarctic blue whale can both get to around 30 metres in length, she said.

Hvalur hf has been contacted for comment.