GAZA, Gaza Strip — An explosion targeted an Israeli military vehicle on the border with Gaza on Saturday and Israeli troops fired into the Palestinian territory, killing four civilians and wounding at least 25, Gaza officials and witnesses said.

Ashraf al-Kadera, a Gaza health ministry spokesman, said all four killed were civilians between the ages of 16 and 18 and that among the wounded were children. Witnesses said that following the large explosion, Israel retaliated with tank and machine gun fire toward residential areas at the al-Muntar hill in the central part of the territory, hitting people who were returning from a funeral east of Gaza City.

The Israeli military said they were investigating the incident and had no further comment. But military officials speaking anonymously because they were not permitted to discuss the incidents said Gaza militants fired an anti-tank missile toward an Israeli jeep that was patrolling along the border.

Gaza militants often fire rockets from the Israel-Gaza border area toward nearby Israeli communities and low-level clashes with the Israeli military are common.

In a text message to reporters, Hamas spokesman Fawzi Barhoum threatened to respond.

"Targeting civilians is a dangerous escalation that cannot be tolerated. The resistance has the full right to respond to the Israeli crimes," he said.

Rami Harra said his 17-year-old brother Muhammad Harra was killed in the strike.

"He was at home when the explosion took place. He went out to see what happened and when he started to help evacuating wounded people who were on the ground another shell hit the place and killed him," he said outside the morgue. "Why did they kill him? I can't believe my eyes that I am seeing his dead body."

Israel carried out a broad military offensive in Gaza nearly four years ago in response to years of near daily rocket fire. Major salvos from Gaza have subsided since then, but sporadic rocket fire has continued.

Gaza's Islamist Hamas rulers have largely refrained from rocket attacks since the devastating Israeli military offensive that killed hundreds of Palestinians.

Hamas, which has killed hundreds of Israelis in suicide bombings and other attacks, remains virulently anti-Israel in its rhetoric but has sought to keep things quiet as it consolidates control of Gaza, which it seized five years ago during a brief civil war against the rival Fatah movement.

Still, it is under pressure from smaller groups to prove that it remains in confrontation with the Jewish state.

The territory is home to numerous militant groups, including murky al-Qaida-inspired organizations that do not answer to Hamas. Gaza has also been flooded with weapons in recent years, many of them believed to have been smuggled from northern Africa and into Gaza through tunnels under the Egyptian border.