Archaeologists in Jerusalem have uncovered an ancient clay fragment dating back some 3,400 years, the oldest-ever sample of writing found in the Holy City, Israeli researchers said today.

The tiny fragment measures two centimetres by 2.8 cm (about one square inch) and is covered with cuneiform script, the earliest known form of writing in the world.

The clay chip is a key find which indicates the importance of the city in the Bronze Age, around 1,400 BC, researchers at Jerusalem's Hebrew University said.

It was discovered during an excavation in an area just south of the walls of the Old City in Israeli-annexed east Jerusalem.

The miniscule chip is believed to have been part of the royal archives and indicates the importance of Jerusalem as a major city in the late Bronze Age, the Hebrew University said in a statement.

The clay fragment was found by researchers sifting through debris removed from beneath a tower from the 10th century BC.

According to an expert from the university's Institute of Archaeology, the script on the fragment, which contains snippets of words such as "you were" and "them," appears to have been very carefully formed.

"It was written by a highly skilled scribe who, in all likelihood, prepared tablets for the royal household of the time," said professor Wayne Horowitz, an expert in Assyriology who deciphered the script.

Researchers believe the tablet may be part of a "royal missive" sent from the Canaanite ruler of Jerusalem to the Egyptian Pharaoh Amenhotep IV (better known as Akhenaten), who lived in the 14th century BC.

The fragment dates back to the same era as 380 tablets discovered in the Egyptian site of El-Amarna that are believed to be part of Akhenaten's archives.

Before now, the oldest sample of text ever discovered in Jerusalem was a tablet found in the Shiloah water tunnel in the same area that dates back to the eight century BC reign of the biblical King Hezekiah.

The tiny clay fragment predates that tablet by about 600 years.