Saudi Deputy Crown Prince Mohammed bin Salman, who is also defence minister, announced the new coalition in December.
A Western diplomat said at the time that details of how the grouping would work remained unclear and "they don't have the infrastructure" yet to run such a coalition.
"This is official now, that they will meet end of March," the Saudi source said, without giving a date.
The source added that the coalition now has 35 members, up from the 34 announced initially.
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Saudi Arabia said the alliance would share intelligence, combat violent ideology and deploy troops if necessary.
The kingdom is a member of the US-led coalition that has been bombing the Islamic State group in Iraq and Syria for more than 18 months.
On Monday, Saudi Foreign Minister Adel al-Jubeir said his country was ready to deploy special forces to Syria if the coalition decides to begin a ground operation.