LINCOLN, ENGLAND (REUTERS) - Sniffer dogs are a vital tool for bomb detection.

But modern explosives contain increasingly varied ingredients, making detection harder.

A British study funded by the US Office of Naval Research could help train the next generation of sniffer dogs.

University of Lincoln researchers found that dogs can categorise odours and apply this knowledge to scents they have not smelt before.

Dr Anna Wilkinson from the School of Life Sciences at the University of Lincoln, said: "If something smells fishy you don't have to smell every fish to know that something smells fishy.

"And so what we wanted to do, we wanted to see if they could learn that sort of category. And as humans we naturally do that because we give labels to things and we say 'oh, that's fishy', but animals can't do that in the same way. But if you can train them in such a way to use that sort of categorical type of information it makes them much better at learning and it also in general helps animals remember it as well."

In lab tests, dogs split into two groups were trained to respond to 40 different smells.

Dogs in the experimental group were rewarded for responding - by either lying down or sitting - when presented with smells which fit a specific category, and for not responding to other non-category stimuli.

Says Dr Wilkinson: "We presented them with novel odours which belonged to the category that they had never come across before. And they responded to them as if they were their training stimuli - so in the same way as they did to their training stimuli."

Surprisingly, the dogs could still place odours in the correct category six weeks later.

It could have a profound impact on how detection dogs are trained.

The Office for Naval Research told Reuters it is developing ways to train dogs to better tackle the challenges of modern explosives.