JERUSALEM — Israel and the militant group Hamas seemed set on a collision course Monday, with an escalation of cross-border clashes around the Gaza Strip, Hamas vowing to avenge the deaths of six of its fighters, and Israeli warplanes attacking dozens of targets in the Palestinian coastal territory.
Lieutenant Colonel Peter Lerner, a spokesman for the Israeli military, said the army was completing the deployment of two infantry brigades along the border with Gaza, and the government had approved the call-up of 1,500 reservists, mainly Home Front Command and aerial defense units.
“If last week we were talking about calm being answered by calm,” Lerner said, “we are now talking about preparing for an escalation.”
Early Tuesday, the Israeli Defense Forces announced on Twitter they had “commenced Operation Protective Edge in Gaza against Hamas in order to stop the terror Israel’s citizens face on a daily basis.”
According to a Reuters report, predawn airstrikes had hit at least 30 targets in Gaza, including homes of suspected militants.
Capitalizing on broader Israeli-Palestinian tensions following the kidnapping and killing of three Israeli teenagers in the West Bank last month and the grisly revenge killing of a Palestinian teenager in Jerusalem last week, Hamas called for a mass demonstration Monday night in the volatile West Bank city of Hebron.
Hundreds of protesters scuffled with Palestinian Authority security forces and threw stones at them.
The developments were likely to further undermine Hamas's recent reconciliation pact with the more moderate Palestinian Authority leadership based in the West Bank, which has been urging calm rather than protests. Intended to heal a seven-year split between the West Bank and Gaza, the pact resulted in a new government, but little else.
The tit-for-tat Palestinian rocket attacks and Israeli airstrikes continued through Monday. Hamas said that five of its fighters were killed by an Israeli airstrike on a tunnel used for “resistance” against Israel in southern Gaza and another was killed in a separate air attack. Another militant who was trapped in the tunnel and presumed dead was found wounded but alive.
Lerner said the air force attacked the tunnel a couple of days ago and when the Hamas militants entered it Sunday night, possibly to use it for an attack on Israeli forces, it collapsed or exploded on them.
These were Hamas’s heaviest losses in months. Sami Abu Zuhri, a spokesman for the movement, said Israel “will not go unpunished for this crime.”
Two more Gaza militants, believed to belong to a radical Salafi group, were killed in an Israeli airstrike Sunday night. Israel said they had been involved in the recent rocket fire.
Ashraf al-Qedra, a spokesman for the Health Ministry in Gaza, said that 15 people, including five children, were also wounded in Israeli airstrikes late Sunday and early Monday.
About 80 rockets and mortar shells fired from Gaza struck southern Israel on Monday. One reached deep into Israeli territory, crashing into open ground near Beersheba, about 25 miles from the border with Gaza. A soldier was wounded by shrapnel.
Hamas’s military wing claimed responsibility for firing dozens of rockets into Israel for the first time in this latest round of hostilities that began three weeks ago.
In a short video clip, the Hamas military wing accused Israel of bringing death and destruction to Gaza and warned the residents of Beersheba to flee “before it is too late.”
Yaakov Peri, an Israeli government minister, told reporters Sunday that there had been efforts by Egypt, Jordan, and Turkey to restore an Egyptian-brokered cease-fire. Mushir al-Masri, a Hamas official in Gaza, said his movement had received no cease-fire request from any side.
Also Monday, Avigdor Lieberman, Israel’s foreign minister and leader of the ultranationalist Yisrael Beiteinu party, broke off his 20-month alliance with the conservative Likud Party led by Prime Minister Benjamin Netanyahu, citing “fundamental disagreements” between the two. Lieberman has urged much tougher action against Hamas and Gaza.
The tensions along Israel’s border with Gaza began with the kidnapping of the three Israeli teenagers — Eyal Yifrach, 19; Gilad Shaar, 16; and Naftali Fraenkel, 16 — on June 12. Israel blamed Hamas for their abduction and conducted a broad clampdown against Hamas’s infrastructure in the West Bank.
After the killing Wednesday of the Palestinian teenager, Mohammed Abu Khdeir, 16, street clashes between young Arab protesters and Israeli security forces flared in parts of East Jerusalem and in Arab towns across Israel, though the West Bank remained largely quiet.
Netanyahu spoke by telephone with the teen’s father, Hussein Abu Khdeir, on Monday, a day after Israeli authorities arrested six suspects, all Israeli Jews and three of them minors, in the killing.
“I would like to express my outrage and that of the citizens of Israel over the reprehensible murder of your son,” Netanyahu said, according to a statement from his office.