PROVIDENCE, R.I. (AP) _ Rhode Island health officials say they believe 10 people have died since March after using a new and illegal synthetic opiate.

The health department said Friday that most of those who died are from northern Rhode Island. Officials believe they were all intravenous drug users.

Health Director Michael Fine tells The Associated Press that about 250 people die each year in Rhode Island after overdosing on opiates. About half were using prescription opiates.

Fine says investigators want to identify the chemical makeup of the drug believed to have been responsible for the deaths. The federal Centers for Disease Control and Prevention are assisting in the investigation.

Fine says no deaths have been reported since last month but he worries that whoever manufactured the substance could make more.