The Khartoum government has closed all Iranian cultural centres in Sudan and expelled the cultural attaché and other diplomats, fearing they had become a threat to society, the foreign ministry said on Tuesday.
The expulsions were linked to government concerns that Iranian officials were promoting their Shi'ite brand of Islam in the largely Sunni country.
The Iranian Cultural Centre and its branches had exceeded their mandates and "become a threat to intellectual and social security," the foreign ministry said in a statement.
Sudan, isolated by U.N. and Western sanctions partly linked to its conflict in Darfur, has sought allies and donors across the sectarian divides in the Middle East and further afield.
That has often left it balancing competing interests and loyalties in the complex web of regional rivalries.
Sudan President Omar Hassan al Bashir came to power in 1989 in a bloodless coup backed by Sunni Islamists.
His country turned down an Iranian offer to set up air defenses on its Red Sea coast after a 2012 air strike Khartoum blamed on Israel, fearing it would upset Tehran's regional rival, the Sunni superpower Saudi Arabia, Sudan's foreign minister said in May.
But Sudan, where many people follow the traditional Sufi tradition of Islam, has also received delegations from senior Iranian politicians.
Saudi Arabia, a regional ally of the United States, has been locked in a contest with non-Arab Shi'ite power Iran for influence in the Middle East.
The rivalry has effectively divided the region into two camps, with countries either allied to Saudi Arabia or to Iran.
A government source told Reuters the diplomats had been given 72 hours to leave.