TEHRAN (REUTERS).- Iran accused the British Museum on Monday of breaking a promise to lend it an artifact relating to Cyrus of Persia's conquest of Babylon in the 6th century BC.

Foreign Ministry spokesman Hassan Qashqavi warned of wider harm to archaeological cooperation between London and Tehran if the British Museum did not allow public display of the so-called Cyrus Cylinder in Iran.

A museum spokeswoman said the intention was still to send the piece to Iran once the "practicalities" had been resolved.

Qashqavi suggested that developments after Iran's disputed election in June, which plunged the country into political turmoil, was a reason for museum's reluctance to temporarily hand over the 2,500-year-old clay cylinder.

Iran is already at odds with Britain and other Western powers over the Islamic state's disputed nuclear program. The West suspects it is for military aims. Iran denies this.

"There was an agreement between Iran and the London museum to the effect that the ... cylinder would be lent to Iran for display," Qashqavi told a news conference.

"Unfortunately, the British party did not honor its pledge on illogical, illegal and unethical grounds allegedly due to political developments in Iran," he said. "What does cultural heritage have to do with our domestic political developments?"

Iran's Cultural Heritage Organization has set a deadline of two months, he said. "If within this period this pledge is not honored then all agreements in archaeological research, trade fairs and so on with Britain might be harmed," Qashqavi added.

Esme Wilson, a spokeswoman for the British Museum, said British officials had reiterated their willingness to send the cylinder to Iran at a meeting in England last month.

"There's just a number of practicalities and issues to be resolved. But the intention is still very much to send it, as agreed," she said

She did not specify what sort of practicalities remained to be sorted out or whether Britain would send the cylinder within the two months requested by Iran.

Many Iranians still see Cyrus as one of their greatest historical heroes, who arguably created the first world empire and showed tolerance toward different faiths of his era.

He conquered Babylon in today's Iraq in 539 B.C. and freed the Jews held in captivity there. He is also credited with authoring a decree inscribed on the cylinder named after him which some have described as the first charter of human rights.

(Reporting by Hashem Kalantari and Fredrik Dahl; Additional reporting by Catherine Bosley in London; Editing by Alison Williams)