GAZA CITY, Gaza Strip, (AP) – Israeli tanks and helicopters raided the Gaza Strip on Tuesday, killing the militant son of a Hamas leader and 10 other Palestinians in one of the bloodiest days of fighting since Hamas took over the territory in June.

Palestinian sniper fire across the border killed a volunteer from Ecuador at an Israeli communal farm.

That death, and the killing of Hussam Zahar, 24, the son of hardline Hamas leader Mahmoud Zahar, threatened to fuel the violence at a time when Israel and the Palestinians are trying to move peacemaking into high gear.

At the morgue at Shifa Hospital, Mahmoud Zahar held his lifeless son’s head in his hands and closed his eyes, then kissed him three times on the forehead and recited a verse from the Muslim holy book, the Quran.

Hamas, he vowed, “will respond in the appropriate way. We will defend ourselves by all means.”

Another Zahar son was killed in a botched Israeli assassination attempt against the Hamas leader in his home three years ago.

The operation Tuesday began when undercover Israeli troops moved several hundred yards into the territory to strike an abandoned house east of Gaza City that rocket launchers used, Hamas said.

When Palestinian militants discovered the force, an exchange of fire erupted, the militants said. In the ensuing clashes, Israeli tanks fired at least three shells and aircraft struck twice in the area, Hamas said.

In all, eight Hamas fighters and two civilians were killed by late morning, and 40 Palestinians were wounded, militants and doctors said. Earlier, medical officials had said three civilians were killed.

The Israeli army confirmed an operation in the area, saying troops fired at militants who had approached the border fence. After an exchange of fire broke out, aircraft also fired at the gunmen, the military said.

In the course of the fighting, a Palestinian sniper fired from the border area into Israel, killing a volunteer from Ecuador who was working in a field at the communal farm of Ein Hashlosha, Israeli rescue officials said. Hamas’ military wing claimed responsibility.

Israel has been cracking down on Gaza militants who bombard southern Israel with rockets and mortars and attack troops along the border, even as it seeks peace with the moderate Palestinian government of President Mahmoud Abbas in the West Bank.

“Israel is acting to protect its civilian population from these daily rocket barrages,” Israeli government spokesman Mark Regev said of Tuesday’s operation.

On Monday, Israeli Prime Minister Ehud Olmert suggested Israel would not launch a broad operation in Gaza, despite Defense Minister Ehud Barak’s repeated assertions that a large-scale strike was inevitable.

Abbas’ government, which has controlled only the West Bank since Hamas overran Gaza, condemned the Israeli raid.

“These brutal acts weaken the position of the Palestinian negotiator, in addition to harming the peace process,” spokesman Nabil Abu Rdeneh said.

While violence was swelling in Gaza, Olmert was struggling Tuesday to keep his coalition intact and broad enough to comfortably work toward reaching a peace deal with Abbas’ government.

A hawkish coalition partner, Avigdor Lieberman, is threatening to pull his 11-member Yisrael Beiteinu faction out of Olmert’s government now that Israeli-Palestinian peace talks have started addressing the key issues in the conflict.

A spokeswoman for Lieberman, Irena Etinger, said his party will decide how to act after he meets Olmert on Tuesday.

After a U.S.-sponsored Mideast conference in November, the Israelis and Palestinians relaunched negotiations after seven years of violence, pledging to try to reach an agreement before Bush leaves office a year from now. On Monday, negotiating teams started discussing the thorniest issues, like final borders, shared sovereignty over Jerusalem and the fate of Palestinian refugees from the war that followed Israel’s creation in 1948.

Olmert’s government would still command 67 of parliament’s 120 seats even if Yisrael Beiteinu bolts, but he would be on shaky ground at a time when he would need broadbased support for peace moves. The ultraOrthodox Shas Party has also threatened to leave if Israel agrees to any compromise over Jerusalem, whose eastern sector Israel captured in the 1967 Mideast war. Palestinians claim east Jerusalem as the capital of a future state.