* Protests already closing oil, gas fields
* Army sets up barricades at phosphate plant
* Unrest over jobs often flares in south (Adds riots near Tunis)
By Tarek Amara
TUNIS, May 10 (Reuters) - Tunisia's President Beji Caid Essebsi on Wednesday ordered the army to protect phosphate, gas and oil production facilities after protests aimed at disrupting output broke out in the south of the country.
It is the first time troops in Tunisia will be deployed to protect industrial installations vital to Tunisia's economy. Protests, sit-ins and strikes in recent years have cost the state billions of dollars.
For several weeks, about 1,000 protesters in Tatouine province, where Italy's ENI and Austria's OMV have gas operations, have been demanding jobs and a share in revenue from the area's natural resources.
Protests have also broken out in another southern province, Kebili, and on Wednesday police fired tear gas to break up rioting in a town west of Tunis after a fruit seller set himself on fire in protest against the police.
In an incident similar to the self-immolation in 2011 that sparked the uprising that toppled autocrat Zine El-Abidine Ben Ali, the vendor in Tebourba poured gasoline over himself and set it ablaze. He was hospitalised and rioting erupted.
Six years after the uprising, Tunisia is trying to enact sensitive reforms to help growth, but many unemployed youth in the marginalised south still feel they have gained few opportunities.
The military deployment will take place immediately, Essebsi said.
"It is a serious decision, but it must be applied to protect our resources," he said in a speech to the nation. "Our democratic path has become threatened and law must be applied but we will respect freedoms."
A local resident in the southern Metaloui region - the heartland of Tunisia's phosphate production - said troops arrived in trucks on Wednesday and started setting up barbed wire barricades around facilities.
OMV has taken out around 700 non-essential staff and contractors from its operations in the south as a precaution, and Perenco and Canada-based Serinus Energy have either halted some production or closed gasfields.
Tunisia is a small oil and gas producer compared to its OPEC neighbours Libya and Algeria, with production around 44,000 barrels per day.
Protests that have hit the phosphate sector in past years cost the country more than $2 billion, according to officials. But production has returned to the highest levels since 2010 after officials negotiated deals with protesters.
The government expects to double its phosphate production to 6.5 million tonnes in 2017. (Writing by Patrick Markey; Editing by Robin Pomeroy)