"The solution needed is to stop the fighting between the north and the south," he told reporters.
"If the referendum leads to a renewal of fighting, that is what we fear," said.
He stressed that the referendum, scheduled for January 9, must be fair and free, but reiterated Riyadh's worry that the largest Arab country by territory will be split in half.
He said the Sudan referendum marks "a critical juncture in its history, threatening its territorial division."
The referendum is part of a 2005 peace deal that ended a two-decade-old civil war in Sudan which left an estimated two million dead.
An important aid donor to Sudan and ally to President Omar al-Bashir, Saudi Arabia has repeatedly expressed concern over the referendum without openly stating that it is opposed to it.
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