A confidential 1978 circular shows the United Kingdom’s Foreign and Commonwealth Office had called for the use of the term ‘Persian Gulf’ in all official communications and banned the use of the fake name ‘Arabian Gulf’.

In this circular, which was released by Iranian ambassador to London Hamid Baeinejad on Thursday in a post in his Instagram page, the UK Foreign and Commonwealth Office clearly states that “the correct English name for this stretch of water is ‘Persian Gulf’.”

The confidential document further emphasize that “the term ‘Arabian Gulf’ should never be used in official communications.

On the reason for releasing this directive, the UK government has cited the Iranians’ sensitivity pver the ‘description of the Persian Gulf’, and added, “The use of any other term causes serious offence to the Iranians, and has been known to prejudice contracts and negotiations in Iran.’

Baeidinejad says the document has been taken out of the British government’s archive of classified files thanks to the efforts made by Majid Tafreshi, a senior professor of the Iranian history.

The release of the document comes a few days after Iranian people were outraged by US President Donald Trump’s use of the fake name ‘Arabian Gulf’ when referring to the body of water.