Police posted an officer and increased patrols at Stone Hill Elementary School in Cranston on Thursday after a threat was made against the school.

Cranston Police Chief Col. Michael Winquist on Thursday said the threat came through a letter sent directly to the school.

Based on a “cursory look,” the chief said investigators believe it was authored by the same person who in recent weeks sent a pair of letters to the Johnston Police Department threatening violence against schools in Cranston, Johnston and Warwick. Police will soon have confirmation regarding whether that is the case, he said.

Winquist said police “assess this threat [against Stone Hill] to be very low on the credibility scale,” but are nonetheless taking added precautions.

On Wednesday, Ray Votto, chief operating officer for Cranston Public Schools, also said officials “do not believe [the threat] to be credible” but are following “our usual safety procedures” and working with the Cranston police and Rhode Island State Police.

Neither Winquist nor Votto provided specifics regarding the nature of the threat.

Mayor Allan Fung on Thursday declined to comment on the threat against Stone Hill, other than to say police, city and school officials are “working to ensure it’s a secure environment.”

“We’ve done that from day one,” the mayor said.