MOUNT VERNON, Ohio (AP) — Law enforcement in Ohio shot and killed two men following a nine-hour standoff over the weekend, authorities said.

Knox County sheriff's deputies responded to a report of shots fired at about 11:30 p.m. Friday, and authorities asked residents to shelter in place during the standoff. Officials said negotiators were trying to bring the standoff to a peaceful end.

Captain Jay Sheffer told reporters at about 10 a.m. Saturday that the suspects had been “mobile" about an hour earlier on a side-by-side vehicle, also known as a utility task vehicle or recreational off-highway vehicle.

“When law enforcement attempted to stop the suspects, an officer-involved shooting occurred,” Sheffer said. “Before the shooting occurred one person was extracted safely. After the shooting occurred, one more person was safely removed.”

Emily Morrison, a spokesperson for the sheriff's office, confirmed that both suspects died Saturday, The Columbus Dispatch reported. Their names and other details about them — or the two other individuals involved — weren't immediately released. No officers were injured.

Sgt. Brice Nihiser of the Ohio State Highway Patrol said that the suspects shot at the state patrol helicopter but did not strike it, the Columbus Dispatch reported. He said investigators were trying to determine how many shots were fired during the standoff and where.

“Any time we’re shot at, that definitely escalates things,” Nihiser told the newspaper.

Sheffer said he didn't know what agency the firing officer or officers were with. Multiple agencies had been assisting during the standoff, including the highway patrol and the Ohio Bureau of Criminal Investigation, which will handle the investigation.

Steve Irwin, spokesman for the state attorney general’s office, which oversees the bureau, declined comment Sunday, saying the investigation was still in the early stages, the Columbus Dispatch reported.