TUNIS, Sept 2 (Reuters) - Tunisia's phosphate stocks will deplete on Friday, forcing a halt in exports because of protests at the Gafsa phosphate plant, said Najeh Sellimi, an official at Groupe Chimique a Gabes, the state unit that sells phosphate.

Protesters demanding jobs this week staged sit-ins and caused a stoppage in production. Prime Minister Youssef Chahed has promised a tough line with protesters, after millions of dollars of losses to the state in recent years because of disruptions in phosphate production.

(Reporting by Tarek Amara; writing by Patrick Markey) ((pat.markey@thomsonreuters.com; +213-661-692993; Reuters Messaging: pat.markey.thomsonreuters.com@reuters.net))