GAZA CITY — Israel will target militant groups inside Gaza if violence along the territory’s border with Israel drags on, the chief military spokesman warned on Saturday, a day after 15 Palestinians were killed by Israeli fire in the area’s deadliest violence in four years.

The violence significantly diminished Saturday as just small groups of Palestinians threw stones in several areas near the border fence, drawing Israeli fire that injured 25 people, the Gaza Health Ministry said.

Friday’s mass marches were largely led by Gaza’s ruling Hamas group and touted as the start of a six-week-long protest campaign against a stifling decade-old blockade of the territory.

Prime Minister Benjamin Netanyahu of Israel congratulated soldiers Saturday for allowing the rest of the country to celebrate the Passover holiday safely.