The inspector general for the US Department of Veterans Affairs (VA), Michael Missal, said his office was working with federal law enforcement to "investigate the allegations of potential wrongdoing resulting in patient deaths at the Louis A Johnson VA Medical Center in Clarksburg, West Virginia."

"People at VA have been what looks like the victim of a crime," VA Secretary Robert Wilkie told Fox News, adding he hoped the investigation would be wrapped up quickly.

One of West Virginia's US senators, Democrat Joe Manchin, said his office was made aware of the probe in July 2018, after doctors reported that eight patients had unusually low blood sugar levels for no apparent medical reason.

Manchin said the probe was focusing on a "person of interest" who no longer has contact with patients at the hospital.

This past winter, autopsies on at least two patients in their 80s who died one day apart in April 2018 showed that they had been given insulin injections they did not need. Their deaths were then ruled homicides, local media reported.

Insulin is used to treat diabetes but is dangerous for people who are not suffering from the condition, as it reduces blood sugar levels and, if improperly administered, could lead to a coma or even death.