Experts have dated some of the pottery to about 3,500BC, which could predate by several centuries the writing of the Sumerians of Mesopotamia, who were considered to have invented written language.
The fragments were found at a site called Harappa, which was a small settlement 5,500 years ago but by 2,500BC had developed into an important centre of the Indus civilisation.
Dr Richard Meadow, director of the Harappa Archaeological Research Project at Harvard University in the US, said the simple inscriptions on the shards bore similarities to later Indus writing. But he said he was unable at present to confirm that the symbols were part of a written language. They may represent the contents of the jars or be signs associated with a deity.