Three deaths from overdoses on opioids in Duluth and neighboring Hermantown have been confirmed in the past 48 hours, and authorities said Monday that they fear others could be putting their lives in danger.

"Police are concerned for opioid users and warn of the risk of using these drugs, as their content and purity is often unknown and can cause overdose deaths," the Duluth Police Department said in a statement.

All of the deaths — occurring in three locations — remain under investigation by police in both cities, and authorities were not disclosing any other information for now.

In 2013, the state Health Department reported, 507 Minnesotans died of all types of drug overdoses including 329 in the 11-county metro area.

Deaths from prescribed pain relievers — and illegal heroin, a close cousin in the opiate family — accounted for many of them. By comparison, 374 Minnesotans died on the state's roads last year.

The problem has been acute in St. Louis County, which was already known for having the highest rate of overdose deaths in the state between 2006 and 2010, according to data from the Centers for Disease Control and Prevention. The area sees a lot of prescription painkillers sold, higher than anywhere else except Minneapolis, according to data provided by Carol Falkowski, a drug expert who compiles statistics on Minnesota drug trends.

The trend has both alarmed and frustrated local law enforcement officials, who say they're seeing no easing of arrests and prosecutions resulting from highly addictive opiates circulating underground.

"The guys that are using this need to start thinking about dying from this stuff," said officer Ron Tinsley, spokesman for the Duluth police.

Tinsley declined to reveal any specifics about each death but said the victims "are not just young people."

The officer said he anticipates more will be said about the deaths soon in follow-up statements from his department.

Staff writer Matt McKinney contributed to this report.