Iran is threatening to cut all ties with the British Museum unless the London institution fulfills its promise to loan an ancient artifact, the Cyrus Cylinder, to the National Museum of Iran.

Iran’s state-run Press TV says the museum is using “the post-election political situation in Iran as its main excuse” not to loan the Cylinder, which is dated about 539-530 B.C. and inscribed in Babylonian cuneiform. It has been described as the world’s earliest charter of human rights. An Iranian cultural official says cutting ties with the British Museum would include archaeological expeditions and research.

For its part, the museum says it fully intends to loan the cylinder, adding that it is watching the Iranian political situation to make sure the loan is made under the best possible conditions. The museum had promised to make the loan after its “Babylon: Myth and Reality” exhibition, which ended March 15, and it also wanted the Cylinder shown temporarily in its new Iranian gallery. Discussions on the timing of the loan started only recently, a museum spokeswoman says.