Scientists say they have identified Europe's oldest shoes, sandals woven from grass thought to be around 6,000 years old.

They were among a haul of ancient objects discovered in a bat cave in Spain plundered by miners in the 19th Century, but were analysed in a new study.

Low humidity and cool winds in the cave kept them unusually well-preserved.

Researchers also analysed baskets and a set of tools.

The objects "are the oldest and best-preserved set of plant fibre materials in southern Europe so far known." the study's co-author María Herrero Otal said.

"The technological diversity and the treatment of raw materials documented highlights the skill of prehistoric communities," she added.

New dating techniques used showed that the collection of 76 objects found in the cave was about 2,000 years older than was previously thought.

Some objects in the set date back 9,000 years.

The sandals that were analysed used different types of grass in their structure, researchers said, but also included other materials such as leather and lime.

They date to the Neolithic period, making them older than the 5,500-year-old leather shoes discovered in a cave in Armenia back in 2008.

The cave the 6,000-year-old sandals were found in was the Cueva de los Murciélagos, or the Cave of the Bats, in Andalusia, south-west Spain.

According to the researchers of this study, the cave was first accessed in 1831 by a landowner who collected bat guano, or droppings, used to make fertilizer.

Less than two decades later, it was used by miners who, while mining the cave, discovered a gallery that held partially mummified corpses, baskets, wooden tools, and among others - wild boar teeth and a unique gold diadem.