London's firefighters say sun rays refracted by a Nutella jar likely caused a house fire.

The city's fire brigade says investigators believe the glass jar — which had been emptied of the hazelnut spread — had been placed on a window sill and refracted sunlight, setting blinds alight.

According to a statement posted Tuesday by the brigade, the family was not at home but the blaze killed a dog.

Fire investigator Charlie Pugsley said: "It sounds far-fetched that a jar containing a few rubber bands caused a severe house fire but that's exactly what happened."

The fire happened Feb. 15 in southwest London.