Palestinians gather around the wreckage of a car targeted in an airstrike in Gaza City on Friday. that killed top Palestinian militant commander Zuhair al-Qaissi and a second militant. (Hatem Moussa/AP)

Fifteen Palestinian militants were killed and four Israelis were wounded from Friday to Saturday in a deadly surge of cross-border clashes between the Israeli military and militant factions in the Gaza Strip.

The violent escalation threatened to spark a new wave of warfare along the volatile Gaza-Israel border, where a relatively low-level cycle of reciprocal attacks has become routine. The clashes started Friday morning, when an Israeli airstrike on Gaza City killed the top commander and a second member of the Popular Resistance Committees, or PRC, a militant faction that Israel accused of staging a raid into southern Israel from Egypt’s Sinai Peninsula last August that killed eight Israelis.

The Israeli military said that the commander, Zuhair al-Qaissi, and his group were plotting a similar attack to take place within days.

Gaza-based militants vowed revenge, and they asserted responsibility for a subsequent torrent of more than 100 rockets and mortar shells fired toward southern Israel that wounded four civilians, one seriously. Israel’s anti-missile system deflected at least 27 of the rockets, and most others fell in open spaces, according to Israeli officials, who advised hundreds of thousands of area residents to stay inside and canceled school Sunday.

Israel responded to the rocket fire with multiple airstrikes on what it said were weapons factories and rocket-launching squads in Gaza. Some hit heavily populated areas in the crowded coastal enclave, and at least 20 people were injured, several of whom were civilians, Gaza medics and witnesses said. Five of those killed were PRC members, and 10 were fighters with the Islamic Jihad militant group, according to militants and medics in Gaza.

“We will continue to hit whoever plans to attack citizens of the state of Israel,” Israeli Prime Minister Benjamin Netanyahu said Saturday.

Hamas, the Islamist organization that rules Gaza, condemned the airstrikes, as did neighboring Egypt, whose foreign minister said he was “exerting efforts and making crucial calls” to end the clashes, according to Egyptian media. Hamas says it does not fire rockets into Israel, but the Israeli armed forces said Saturday that the group “enables” firing by other Gaza-based militant factions and would “bear the consequences.”

“The Palestinian people have the right to defend themselves,” said Taher al-Nunu, a Hamas spokesman, who called on the international community to “quickly stop the Israeli aggression over our people.”

The PRC, in cooperation with Hamas, abducted an Israeli soldier, Gilad Shalit, in 2006. Shalit was freed last year in exchange for more than 1,000 Palestinian prisoners.

Matan Vilnai, Israel’s home front defense minister, told reporters Saturday that Hamas was working to rein in the rocket fire in a bid to avoid a repetition of the large-scale Israeli military assault on Gaza three years ago. That war weakened Hamas’s combat infrastructure, but the Israeli military says the group has steadily rebuilt its weapons stockpile since.

Israel is building a fence along its southern border with Egypt that was originally intended to prevent the entrance of African migrants and asylum-seekers. But Israeli authorities say they now view it as a key measure to thwart attacks emanating from the desolate and loosely patrolled Sinai.

Abdulkarim reported from Gaza.