Iranian President Hassan Rowhani said on Wednesday Saudi Arabia should be punished for its role in a deadly stampede at last year's Hajj pilgrimage.
"The countries in the region and the Islamic world should band together and punish the Saudi government," Rowhani said, days before this year's Hajj is set to attract millions to holy sites in Saudi Arabia.
He accused the Saudis of incompetence in last year's handling of the event.
The regional rivals have traded blame for a stampede at the 2015 Hajj that claimed around 2,000 lives, based on a dpa tally and other independent reports. The Saudis had placed the death toll at 769.
Rowhani's comments come just days after Iran's Supreme Leader, Ayatollah Ali Khamenei, criticized the Saudis as unbelievers and questioned the country's role in administering the annual pilgrimage to Mecca.
A senior Saudi religious official hit back in equally heated terms on Monday, saying that the Iranian comments were not surprising as they were "not Muslims."
It was not clear whether the Mufti of Saudi Arabia, Abdul-Aziz Al al-Sheikh, was referring to the Iranian leadership or the country's Shiite population as a whole in his comments to the Makkah newspaper.
Al al-Sheikh told the newspaper: "They are the sons of the Magi, and their enmity towards the Muslims and in particular the Sunnis is of long standing."
The reference to the Magi, a term used for the Zoroastrian religion which dominated Iran before the coming of Islam, is also typical of anti-Shiite rhetoric used by Sunni extremist groups such as Islamic State and al-Qaeda.
In Islamist thought, condemning other Muslims as unbelievers is generally held to be unacceptable, but Saudi Arabia's puritanical Wahhabite school of Sunni Islam and the Shiite sect, which is a minority across the Islamic world but a majority in Iran, tend to see each other as beyond the pale.
The two countries are pitted in a long-standing rivalry for dominance in the Gulf region which has seen both seeking to exploit sectarian feelings, as well as backing opposing sides in civil wars in Syria and Yemen.
In 2015, more than 2 million pilgrims travelled to Mecca, the birthplace of the prophet Mohammed. All devout Muslims are expected to perform the Hajj at least once in their lifetime, provided they are fit enough and have the financial means to do so.