JERUSALEM (Agence France-Presse)  Israeli warplanes killed three Islamic militants on Sunday, Israeli and Palestinian officials said, and Prime Minister Benjamin Netanyahu warned that the military would respond harshly to rocket and mortar fire from Gaza.

The airstrike struck a group of gunmen in the central Gaza Strip, killing them with an air-to-ground missile, Palestinian medics said. The Israeli military said the three militants were hit “as they were preparing to fire rockets into Israel.”

The air raid, east of Deir el-Balah in central Gaza, followed a period of relative calm since Israel ended an offensive into Gaza a year ago in response to rocket fire. It came hours after four mortar rounds hit southern Israel, though without causing casualties.

Mr. Netanyahu warned earlier on Sunday that Israel would react quickly to any renewed rocket and mortar attacks from Gaza, which is governed by the Islamist movement Hamas. He said more than 20 rockets and mortar shells had been fired in the past week.