Whalers in Iceland have killed what appears to be a blue whale, one of the largest creatures left on the planet.

Photographic evidence from campaigners opposed to whaling show a large animal being butchered for export.

Several experts have concluded from these pictures that it's a juvenile male blue, a species that hasn't been deliberately killed since 1978.

The whaling company involved say they are confident that the animal is a hybrid between a blue and fin whale.

DNA testing will be needed to confirm the whale's true identity.

Why does the species matter?
The key reason for interest in the species is to determine whether this killing is legal or not under Icelandic law.

Weighing as much as 200 tonnes and stretching up to 30 metres, blue whales were hunted to the brink by commercial whalers from many countries including the UK from the 1940s to the 1960s when they became a protected stock under the International Whaling Commission. That means that all countries, including Iceland agreed not to kill the creatures.

It's different for fin whales. While there is an international moratorium on killing all whales, Iceland doesn't agree that fin whales are threatened and gives permits for their hunting.

Hybrids between fin and blue whales are a grey area, say specialists. A hybrid allows the whalers to say they simply made a mistake.

"If this is a blue whale, it would be illegal and a breach and there could be fines and perhaps the company might lose their licence to hunt whales," said Arne Feuerhahn, from campaign group Hard to Port, which documented the latest killing.

What do experts think?
From the photographic evidence, most seem to be of the view that it is a blue whale.

"We cannot confirm 100%," said Arne Feuerhahn.

"We have consulted a lot of international experts, most think that it is a juvenile male blue whale but there also has been some doubts with some believing that it could be a hybrid between a blue and a fin whale."

Others were more definite.

"From the photos, it has all the characteristics of a blue whale," Dr Phillip Clapham, from the US National Oceanic and Atmospheric Administration (NOAA) Alaska Fisheries Science Centre, said in a statement.

"Given that, notably the coloration pattern, there is almost no possibility that an experienced observer would have misidentified it as anything else at sea."

What do the whalers say?
The company involved is certain that the animal it has killed is not a blue whale but a hybrid.

"I am absolutely confident that it's a hybrid," said Kristján Loftsson who runs Hvalur hf.

"To mistake a blue whale for a fin whale is impossible, this whale has all the characterisations of a fin whale in the ocean. There are a lot of blue whales off the Iceland coast, when we see the blows and sail to it, and we realise it is a blue and then we leave it and go and look for fin whales."

What have the Icelandic government said?
Kristján Thor Juliusson, Iceland's Minister of Agriculture and Fisheries, said: "While initial information suggests that the animal in question was not a blue whale, we take these reports seriously and the relevant authorities are investigating this matter with all urgency.

"At present, Icelandic authorities are not in a position to confirm the species, although initial information from the directorate of fisheries in Iceland suggests the animal caught is not likely to be a blue whale but rather a hybrid of a fin whale and a blue whale.

Campaigners believe that whether it's a blue or a hybrid won't matter that much in the long term as the overall impression in their view is negative.

"These images leave people around the world speechless - thousands come to Iceland to see these animals in the wild and there is just one company who keep this industry alive in Iceland. It really shines a bad light on Iceland's reputation internationally," said campaigner Arne Feuerhahn.

Will DNA testing be definitive?
Yes it's likely that it will be. But there are doubts among campaigners that this will happen swiftly.

"We've been contacting the Icelandic authorities and requested samples," said Arne Feuerhahn.

"But it looks right now that they are not really bothered as they have said it could be fall or winter before they get the results of DNA tests."

The Icelandic government say they are not dragging their feet on this issue..

"This will only be confirmed once a DNA analysis has been concluded, a process that is being expedited due to the nature of these reports," said Minister Kristján Thor Juliusson,

Are hybrid blue whales common?
Specialists believe that hybrids are not very common in the waters off Iceland.

"Since 1983, they've only recorded five of them," said Astrid Fuchs from the charity, Whale and Dolphin Conservation.

"Four of them have been killed by whalers and one is a very beloved whale watching object and is still alive - they are very rare," she told BBC News.

What will happen to the whale meat?
Iceland sells almost all of its whale meat to Japan one of a handful of countries that reject the international consensus to protect whales. However, if this whale is a blue then this meat can't be legally shipped anywhere.

If it turns out to be a hybrid whale, then it is possible that it could be sold in Iceland. However, under the international regulations that govern animal trading, it is the status of the hybrid parents that matter - so if it has blue whale parentage, the Japanese market would be closed.

What are the implications for Icelandic whaling?
Kristján Loftsson's company has already captured and killed 22 whales including this recent and most controversial one.

If it turns out to be a hybrid, then it is likely there won't be major repercussions for the whalers.

Mr Loftsson says he is being targeted by campaigners and there is nothing unusual about the recent killing.

"This is nothing new to us, we have had at least five in previous years with similar characteristics and DNA analysis shows a completely different profile from a fin whale and that has been described as a hybrid of a blue and a fin," he told BBC News.

Campaigners, though, believe it could be the beginning of the end.

"We hope it might be the nail in the coffin of Icelandic whaling," said Astrid Fuchs from WDC (Whale and Dolphin Conservation).

"It confirms what scientists have been saying for years, whaling can't be regulated - it is always a bit out of control, they are going out there but they don't know what they are shooting. If this is a blue it would drive home the message that you can't regulate this."