The Cyrus Cylinder, a 6th century B.C. clay tablet which is thought to be the world's earliest bill of rights. (detail).

Iran said it will cut ties with the British Museum on Monday because of the museum's failure to lend Tehran an ancient Babylonian artifact described as the world's earliest bill of rights.

The spat over the loan has long festered between London and Tehran, and comes against the backdrop of increasingly tense Iranian-British relations.

Tehran is under heavy pressure from the West over its nuclear program, and has accused Britain and other foreign governments of interference in domestic policies and of stoking the country's postelection street protests.

The artifact is a 6th century B.C. clay tablet with an account in cuneiform of the conquest of Babylon by Persian King Cyrus the Great. It describes how Cyrus conquered Babylon in 539 B.C. and restored many of the people held captive by the Babylonians to their homelands.

Called the Cyrus Cylinder, it has been described by the U.N. Web site and elsewhere as the world's oldest human rights document.

According to officials in Iran, the piece was to have been lent to Tehran by Sunday for an exhibition agreed on by the museum and the Iranian government.

Vice President Hamid Baqaei, who is also the head of Iran's cultural heritage and tourism organization, was quoted by state Press TV as saying that the ties would be cut on Monday. It wasn't immediately clear if this has happened.

Baqaei said the British Museum's failure to keep its promise is "not acceptable."

He said the British Museum initially was to lend Tehran the Cyrus Cylinder last September but postponed the deal, citing technical reasons and the postelection unrest following Iran's disputed June presidential election.

"The Cyrus Cylinder has been turned from a cultural issue into a political one by the British," Baqaei said, adding that Iran "will sever all its ties with the British Museum, which has become a political institution."

Baqaei said Iran would send a protest letter the U.N. education agency, UNESCO, over the matter.

In October, British Museum spokeswoman Esme Wilson said the museum was preparing to send a member of staff to Tehran to discuss the loan.

In London, calls put in to the British Museum by The Associated Press were not immediately answered.