A previously unknown civilisation was using writing in Central Asia 4,000 years ago, hundreds of years before Chinese writing developed, archaeologists have discovered.

An excavation near Ashgabat, the capital of Turkmenistan, revealed an inscription on a piece of stone that seems to have been used as a stamp seal.

The discovery suggests that Central Asia had a civilisation comparable with that of Mesopotamia and ancient Iran as far back as the Bronze Age, University of Pennsylvania archaeologist Fredrik Hiebert told the BBC.

The area had been studied by Soviet archaeologists before, but had been inaccessible to Western researchers until recently, he said.

The ancient society is believed to have herded goats, grown crops and made bronze tools and ceramics, all some 300 years after the pyramids of Egypt were built.

Name unknown

It is not known what the people of the civilisation called themselves, so researchers have dubbed the society the Bactria Margiana Archaeology Complex (B-Mac), after the ancient Greek names for the two regions it covers.

The recent findings suggest that the region - which became the heart of the Silk Road from China to the West 2,000 years later - was integrated into surrounding societies centuries earlier than previously believed.

Archaeologists have uncovered "monumental structures", including multi-roomed mud brick buildings like apartment complexes.

Mr Hiebert discovered the stamp seal in June of last year and presented it at seminars at the University of Pennsylvania and Harvard University in the past week.

It is believed to date from 2300 BC, at a time when literate civilisations existed in Mesopotamia, Iran, and the Indus River Valley.

The symbols on the seal may be related to ancient Chinese, but China is not believed to have developed writing at the time the artefact was made.