JAKARTA (Reuters) - The death toll from a fire at an Indonesian nickel smelter has risen to 18 as of Tuesday from 13 on Sunday, local police said, while operations at the smelter remain suspended as authorities investigate the cause of the incident.

Fire broke out early on Sunday morning at a nickel smelter furnace on Sulawesi island owned by Indonesia Tsingshan Stainless Steel (ITSS), a unit of China's Tsingshan Holding Group.

Indonesia, the world's biggest nickel producer, has banned unprocessed nickel ore exports while promoting major investments in smelting and processing, but several fatal accidents have hit the sector in recent years.

President Joko Widodo, while identifying nickel processing as a priority for economic development, has called for improved safety and enhanced monitoring of environmental standards.

Central Sulawesi police spokesperson Djoko Wienartono said on Tuesday that the victims included eight foreign workers, and that the police are still investigating the cause of the fire. China's foreign ministry said four Chinese were among the initial 13 confirmed dead.

A spokesperson for the Indonesia Morowali Industrial Park where the plant is located, Dedy Kurniawan, said on Tuesday that operations would remain suspended during the investigation.

(Reporting by Fransiska Nangoy; Editing by Edmund Klamann)