JAKARTA (Reuters) - Indonesian government said on Tuesday there was a strong indication of a safety procedure violation that led to a fire at a nickel smelter on Sulawesi island that killed 21 workers.

       A fire broke out on Dec. 24 at a furnace in a smelter operated by Tsingshan Stainless Steel Indonesia, located in the country's largest nickel hub, the Indonesia Morowali Industrial Park (IMIP).

       There was a strong indication of standard procedure violation and negligence in the implementation of safety requirements that allegedly led to the fire incident, Manpower Minister Ida Fauziyah said in a statement on Tuesday.

       She did not elaborate on the suspected violations.

       In the same statement, Central Sulawesi police chief Agus Nugroho said the police were investigation into the cause of the fire.

       Indonesia, the world's biggest nickel producer, has banned exports of unprocessed nickel ore as it moves to boost domestic smelting and processing, but the sector has suffered several fatal incidents in recent years.

       Senior cabinet minister overseeing the mining industry, Luhut Pandjaitan, called for law enforcement to take firm action to avoid similar incidents .

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       "We have to show that we do need investment, but they have to comply with regulations in our country. They cannot ignore the rules," Luhut said.

       IMIP spokeperson Dedy Kurniawan said the companies within the industrial park comply with government regulations.

       (Reporting by Fransiska Nangoy, additional reporting by Stanley Widianto, Editing by Louise Heavens)