CHARLESTOWN, R.I. (AP) – Charlestown police have been unable to identify a suspected toxic substance that sent four people to the hospital Sunday.

But Michael Sweeney, chief of investigations for the state fire marshall’s office, said it appears to be part of a Molotov cocktail, which is a makeshift explosive.

Charlestown police said Tracy Ready backed over a jar containing the liquid in her driveway, then got it on her hands.

A friend of Ready was exposed to the liquid, which Ready said caused a burning sensation.

Two police officers who responded to the scene were overcome by fumes.

All were treated and released at a local hospital.

Tests by the state couldn’t determine what it was. Police said it may have been diluted by rainwater. The incident is under investigation.

AP-ES-01-01-08 1438EST