In a rare act of diplomatic accord between the UK and Iran, the British Museum has sent the Cyrus Cylinder – one of its most culturally significant possessions – to Tehran where it will remain on loan and be displayed for the next four months.

The prized clay artefact, a document written by the Persian king Cyrus the Great, was flown to the Iranian capital on Thursday night and will go on display at the National Museum of Iran on Sunday.

The cylinder, written in Babylonian cuneiform after Cyrus’s conquest of Babylon in 539 BC, has been described as the first declaration of human rights. It records Cyrus’s restoration, after his conquest, of shrines dedicated to different gods, and his repatriation of deported peoples.

Neil MacGregor, director of the British Museum, said the loan was especially important at a time of diplomatic tension between Iran and the west.

“This is a document that speaks of respect for the rights of other peoples and of different ways of worshipping,” he said. “It is very hard to look at the Cyrus Cylinder without being reminded of that view of government and human relationships.”

He pointed out: “The Cyrus Cylinder is a history of the Middle East in one object. At this moment, the loan has an extraordinary value. This is an object that links the histories of Iran, Iraq and Israel. Cyrus was a major figure in the Jewish and Christian traditions.”

The loan brings to an end a row between the Iranian government and the mu­seum, which was accused of dragging its feet over the loan earlier this year.

The museum had agreed to lend the cylinder to Iran after it borrowed several works from Iranian museums for its acclaimed exhibitions on ancient Persia in 2005 and on the Iranian emperor Shah Abbas last year.

The loan was due to take place in January. But the museum postponed it at the last minute when it discovered two fragments of inscribed clay in a drawer that offered vital clues to how the cylinder was copied and disseminated.

The Iranian government became convinced the delay was politically motivated, and its Cultural Heritage Organisation cut all relations and co-operation with the museum in February.

The museum defused tensions by inviting Iranian scholars to study the newly discovered fragments at an international workshop, and insisted the loan would go ahead. The fragments will also be displayed in the exhibition in Tehran.

Mr MacGregor said he was confident the loan was secure, despite the troubles that have afflicted Iran since last year’s contested presidential election.

He said: “The loans that the museums of Iran made to us for [our] exhibitions included some of the most important national treasures they hold. They showed remarkable trust, given the long history of difficulty and suspicion between the two countries, and they were severely criticised in the Iranian media. We want to reciprocate that trust. They have given us matching promises to those that we made.”

He also defended the loan against critics who believe it inappropriate to have cultural relations with a country with a questionable record on human rights.

“An object that speaks of dialogues between nations and religions is more appropriately lent now that at any point in the last generation,” he said. “The trustees take the view that it is always important that cultural relations and the dialogue of scholars continue, irrespective of any political difficulties.”

Baroness Helena Ken­nedy, one of the museum’s trustees and a human-rights lawyer, said: “Art and culture can sustain relationships between the people of nations, even when diplomacy is strained.

“To present this particular temporary gift to the people of Iran at this particular time is an act of faith which will have profound meaning and value.”

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