An attempt to smuggle a Babylonian treasure into Britain has been foiled after it was seized at Heathrow airport.

The inscribed cuneiform stone antiquity, which is about 30cm high, had been looted from Iraq. Dating from the second millennium BC, it is worthy of the world’s greatest museums and valued at hundreds of thousands of pounds.

A Border Force officer’s suspicions were raised by a declaration that the cargo contained a “carved stone for home decoration” made in Turkey and valued at “300” in an unspecified currency.

After Googling the object, the officer contacted the British Museum, having discovered that its collection boasted one of the few surviving examples of a Babylonian kudurru, an official document drawn up on the instructions of the Babylonian king to record the gift of lands or other benefits bestowed on particular individuals.

Later this month the British Museum will stage the object’s official handover to Iraq.

The stone dates from the reign of King Nebuchadnezzar I (about 1126-1103BC). Photograph: British Museum

Dr St John Simpson, a senior curator at the British Museum, told the Guardian: “It’s a museum-quality piece. Even though it’s broken, it should be on display in a museum.

“Declaring it as ‘carved stone for home decoration’ was being economical with the truth, as they say. A decorative ornament for a rather hefty mantelpiece. It is a very heavy object.”

It dates from the reign of the Babylonian king Nebuchadnezzar I (about 1126-1103BC), not to be confused with his famous later namesake Nebuchadnezzar II (605-562BC).

This ruler is practically unknown beyond his victory over the kingdom of Elam in present-day Iran, when he recovered the cultic idol of the Babylonian state god, Marduk. The kudurru’s inscription refers to a military campaign, perhaps that very one.

Simpson said: “It’s a historical document, a primary document for a little-known episode of Mesopotamian history, showing the relationship – not always friendly – between neighbours.”

The cuneiform stone contains two columns of text written in the Babylonian language. They are difficult to interpret as the object is broken and its central portion is worn away. It must originally have been placed in a temple, as its concluding lines contain curse formulae to safeguard the monument.

Simpson said: “Importantly, this kudurru has been neither previously recorded nor published and must therefore come from illicit digging at a site in southern Iraq. The text mentions the god Enlil and the goddess Gula and refers several times to the city of Nippur, in southern Iraq, where Enlil was the chief god. This makes it quite likely that this kudurru originates from Nippur or its close vicinity.”

He noted that many archaeological sites in southern Iraq were badly looted between 1994 and 2004, during which time he suspects this kudurru was removed. The whereabouts of its lower half are unknown. “Hopefully, it is still in the ground somewhere in Iraq and may one day be found by archaeologists.”

The object has been declared crown property after the British importer failed to demonstrate legal title. Investigations are continuing.

On 19 March the British Museum will formally hand it over to the Iraqi embassy in London, to be transferred to the Iraq Museum in Baghdad, which is now fully restored and open to visitors.

Asked whether looting was still occurring in Iraq, Simpson said: “The situation in Iraq is actually good now. They have a system of archaeological police who are armed, who patrol and who are responsible for the protection of all sites that are currently being excavated. They also patrol the unexcavated ones.”