Palestinian presidential candidate Mahmoud Abbas (search) denounced Israel as the "Zionist enemy" Tuesday — his harshest language yet on the campaign trail — after Israeli tank shells slammed into a strawberry patch, killing seven Palestinians, many of them children.

Israel insisted their shells hit militants who were firing mortar rounds at Israeli targets, but relatives and witnesses said the dead were children and teenagers, and a senior army commander apologized for civilian casualties. It was the bloodiest strike in Gaza in three months.

Abbas' rhetoric has grown increasingly hard-line during a four-day campaign swing through Gaza as he reached out to younger, more militant Palestinians ahead of Sunday's election.

But his comments condemning Tuesday's deaths were his most inflammatory.

"We came to you today, while we are praying for the souls of the martyrs who were killed today by the shells of the Zionist enemy in Beit Lahiya," Abbas told thousands of supporters, using a term for Israel usually employed by Islamic militants.

In response, Israeli Foreign Minister Silvan Shalom (search) broke with his government's policy of not criticizing Abbas during the campaign.

"Israel is very concerned about Abu Mazen's recent statements which are very militant ... and the like of which we haven't heard in a long time," he said, referring to Abbas by his nickname.

In Washington, the State Department responded with strong criticism.

"Obviously, we find such language disturbing," said Rhonda Shore, spokeswoman for the Bureau of Near Eastern Affairs. "Such rhetoric has no place in the process of resuming dialogue and rebuilding trust and confidence between both sides."

Also Tuesday, an Israeli military inquiry exonerated members of an elite Israeli unit in the killing of Palestinian militant Mohamoud Kamil Dobie in the West Bank last month, refuting testimony from a relative that the man was murdered in custody.

The inquiry found that naval commandoes committed "no ethical or moral mistakes" but did not explain how Dobie died.

Dobie's killing had sparked a wave of soul-searching about army behavior during more than four years of fighting with the Palestinians, as human rights groups said rules for use of deadly force are fuzzy and the army is reluctant to investigate the deaths of Palestinian civilians.

Israel considers Abbas a moderate and a pragmatist because of his previous statements against Palestinian violence.

After endorsing the "right of return" for Palestinian refugees and their descendants — a deal-breaker for Israel — and identifying with militants in defiance of an Israeli and U.S. demand that he dismantle violent groups, Abbas on Tuesday introduced another potential obstacle to a peace accord.

Addressing supporters in the West Bank city of Ramallah, Abbas said a peace accord "must get approval in a Palestinian referendum, both here in the homeland and abroad in the exile," granting a veto to millions of Palestinians who do not live in the West Bank and Gaza.

Earlier, in Gaza, Abbas came close to the fighting, with two loud explosions going off as he was about to visit hospitalized survivors of the shelling.

The military said Palestinians were apparently firing homemade rockets at the time. Palestinian security officials said the explosions were Israeli tank shells fired in response to the Palestinian rockets.

The fighting began Tuesday morning, when militants fired mortar rounds that wounded an Israeli woman. Tanks struck back with two shells that slammed into fields as farmers picked strawberries and potatoes, witnesses said.

The military said the shells were aimed at nine masked militants who had been involved in firing the mortar rounds, and soldiers said members of the cell were hit.

However, Dr. Mahmoud al-Asli, director of the Kamal Adwan Hospital in the town of Beit Lahiya, said the dead were between the ages of 11 and 17. He named the seven victims and said six were from the Ghaben family, including three brothers. The family confirmed the names and ages given by the hospital.

Six people were wounded, doctors said. At the Beit Lahiya (search) hospital, the floor of the emergency room was covered with blood.

When the coffins of the three brothers reached the Ghaben home, an aunt, Amina, opened one and smeared blood from the body on her clothes as an act of remembrance. "Is that an adult? It's a child, " she said. "He went in the morning to help his father and brothers pick strawberries."

Members of several militant groups paid their condolences, but none claimed the dead as members.

The Israeli military insisted it was informed by Palestinian liaison officers that six of the seven were 17 and older, and that four or five of them were members of the militant group Hamas.

Lt. Avi Levy, the area army commander, gave a guarded apology. "If we hit innocent Palestinians, I'm sorry for that," he said. "You have to remember that the (militant) groups fire from the cover of these heavily populated civilian areas."

Farmer Yehiye Ghaben, 29, said the incident began when five or six masked men fired rockets from the strawberry patch. Farmers took cover, Ghaben said. As the militants were leaving, Israeli troops fired machine guns and tank shells.

"The only thing I remember were flying body parts and a bloody arm hit my chest," he said, adding that all of those killed were youngsters.

Tuesday's incident was the single deadliest in Gaza since Sept. 30, when an Israeli tank fired a shell at gunmen in the Jebaliya refugee camp in northern Gaza, killing seven Palestinians and wounding 23.

Palestinian militants have stepped up mortar and rocket fire on Israeli settlements in Gaza and border towns in recent weeks as rival militant groups jockey for power ahead of a planned Israeli withdrawal from Gaza in the summer.

In other violence, gunfire erupted early Wednesday at the Erez Israel-Gaza checkpoint where Palestinians were about to cross at the beginning of an Islamic pilgrimage to Mecca, the Israeli military and Palestinian security said. An armed Palestinian was killed.

The military said the Palestinian set off an explosive charge and threw grenades at an Israeli army officer, who shot and killed him. Soldiers exchanged fire with armed Palestinians, and three Palestinian police officers were wounded.

At nightfall Tuesday, Palestinian gunmen attacked an Israeli outpost east of Gaza City. In an exchange of fire, one of the attackers was killed, Palestinian hospital officials said. The military said soldiers returned fire coming from a nearby building.