JERUSALEM - Israeli aircraft struck repeatedly at Palestinian rocket squads in northern Gaza on Wednesday, and one attack that missed its target killed a 12-year-old boy, his father and uncle.

Islamic militants, enraged by the deaths of 19 Palestinians a day earlier, barraged southern Israel with rocket and mortar fire. Among the dead Tuesday was the son of Gaza's most powerful Hamas leader, Mahmoud Zahar. The Islamic group, which controls Gaza, vowed to retaliate.

The boy and his relatives were killed in a strike on a pickup truck east of Gaza City. The Popular Resistance Committees, a small, Hamas-allied faction, said the apparent target was its chief rocket maker, who was driving in the area in a similar vehicle at the time.

Relatives identified the dead as 12-year-old Amir Yazagi, his father Mohammed and uncle Amr, said Dr. Moaiya Hassanain of the Gaza health ministry. Their bodies were so mutilated it was hard to identify them, medics said.

Maj. Avital Leibovich, an Israeli military spokeswoman, acknowledged that the Yazagi family's vehicle was "unintentionally hit."

Civilians regrettably are hurt when militants operate in civilian environments, Leibovich said.

"It is important to me to stress that we have no intention whatsoever to hit or hurt uninvolved civilians," she said.

Hamas spokesman Taher Nunu called the strike "a new crime," saying Israel was "killing more and more of our innocent people and our freedom fighters."

In border communities in southern Israel, the siren warning of rocket attacks rang repeatedly Wednesday morning as 21 rockets and mortars were fired, the Israeli military said. No serious injuries or damage were reported.

Residents of Sderot, a town of 20,000 that is a frequent target, stayed off the streets as sirens blared.

The Islamic Hamas government in Gaza called a three-day mourning period for the 19 Palestinians killed Tuesday, and a general strike took hold across the territory.

Palestinian flags were lowered to half-staff, verses from the Quran, the Muslim holy book, poured forth from mosque loudspeakers, and government offices, banks and shops were shuttered.

Government offices and shops were also closed in the West Bank, which is controlled by Hamas' bitter rival, the moderate Palestinian President Mahmoud Abbas. Leading officials from Abbas' government called Zahar to express condolences, and Prime Minister Salam Fayyad issued his condolences in a statement to the media.

On Wednesday, Iranian President Mahmoud Ahmadinejad called the head of Gaza's government, Ismail Haniyeh, to express his condolences for the death of Zahar's son, Nunu said.

Ahmadinejad accused President Bush of giving Israel his approval for military operations in Gaza during a peacekeeping mission to the region last week.

"Without the green light of the criminal Bush, yesterday's massacre would not have occurred," Ahmadinejad said, according to Nunu.

In West Bank violence, Israeli troops killed the top commander of the militant group Islamic Jihad in a predawn raid on the village of Qabatiya south of Jenin, the group said.

The clashes with Palestinian militants are complicating recently renewed peace talks with Paelstinian moderates in the West Bank that are already fraught with tension over Israeli construction in disputed territory and Palestinian violence.

The negotiations are being held with Abbas' government, which rules only the West Bank. Hamas, which seized control of Gaza in June and rejects Israel's right to exist, is not a party to the talks.