PORTLAND, Maine — Two Portland drivers reported Monday that their windows suddenly shattered while they were behind the wheel.

The shattered windows could all be the result of pellet gun attacks, according to police, who are investigating four such incidents since Oct. 31.

At around 9:40 p.m. Monday, a driver was traveling north on Stevens Avenue when the passenger window shattered as a vehicle passed in the southbound lane, according to police.

A taxi driver reported something similar that night in the same area. That driver was lacerated when two of his vehicle’s windows shattered while he was behind the wheel. Police found a third car parked a few hundred yards away with two broken windows.

Police have not determined if the shattered windows are related to an Oct. 31 incident in which two people riding a tandem bike along Congress Street were shot at with pellets. One of the riders was hit and suffered minor injuries.

Discharging any type of firearm, including gas-powered pellet, airsoft rifles or BB guns, is against Portland city ordinances. Portland Police Chief Heath Gorham said it was fortunate that no one has been seriously hurt.

“These are felony crimes that carry with them serious consequences,” Gorham said.

Portland police investigated two similar complaints in May.

Anyone with information about the suspected pellet gun attacks can contact police at 207-874-8575.