An Israeli air strike on Monday destroyed the Gaza Strip home of a top commander in Hamas' armed wing, killing seven people, including several members of his immediate family, Palestinian medics and local residents said.
The senior Iz al-Din al-Qassam Brigades commander, Maher Zaqout, was not at home at the time, Hamas said.
At least 20 people were injured in the blast, as the Israeli assault on the Hamas-controlled Strip neared the end of its third day.
The strike was followed closely by another aerial assault, this time on a vehicle carrying cooking gas. Medics and witnesses said that five Palestinians were killed and that their bodies were burnt beyond recognition.
Later that night, Israeli aircraft dropped at least 16 bombs on five Hamas government buildings, destroying them, setting fires and sending rubble flying hundreds of meters away, witnesses said. Ambulances raced to the scene. Rescue workers said 40 people were injured.
The three-day death toll rose to at least 320 by Monday afternoon, including eight children under the age of 17 who were killed in two separate strikes overnight, medics said.
Israel launched its campaign, the deadliest against Palestinians in decades, on Saturday, in retaliation for rocket fire aimed at civilians in southern Israeli towns.
Earlier Monday, Four Islamic Jihad members, including senior commander Ziad Abu-Tir, were killed in an Israeli airstrike on the southern Gaza Strip.
Early Monday morning, the IAF obliterated symbols of Hamas power, bombing the Islamic University, closely affiliated with Hamas, and a government compound in Gaza. The Israel Air Force also targeted a house next to the Hamas premier's home, devastating a security compound and flattening a five-story building at a university closely linked to the Islamic group.
Defense Minister Ehud Barak said at a Knesset session Monday that the military was fighting a "war to the bitter end against Hamas."
The strikes have driven Hamas leaders into hiding and appear to have gravely damaged the organization's ability to launch rockets, but barrages continued. Sirens warning of incoming rockets sent Israelis scrambling for cover throughout the day.
One medium-range rocket fired at the Israeli city of Ashkelon killed a Bedouin construction worker there Monday and wounded several others. He was the second Israeli killed since the beginning of the offensive, and the first person ever to be killed by a rocket in Ashkelon, a city of 120,000.
Meanwhile, in in the southern Gaza town of Rafah, Palestinians said a toddler and his two teenage brothers were killed in an airstrike aimed at a Hamas commander.
IAF warplanes bombed Gaza's Hamas-run Interior Ministry on Monday, the first air strike that targeted a government building in Israel's offensive, the Palestinian faction said.
No immediate word was available on whether there were any casualties.
At first light Monday, strong winds blew black smoke from the bombed sites in Gaza City over deserted streets. The air hummed with the buzz of pilotless drones and the roar of jets, punctuated by the explosions of new airstrikes.
Mark Regev, a spokesman for Prime Minister Ehud Olmert, said the military action would go on until the population in southern Israel "no longer live in terror and in fear of constant rocket barrages".
"(The operation could) take many days," said Israel Defense Forces spokesperson Avi Benayahu.
At least 51 civilians in the Gaza Strip have been killed in Israeli air strikes since Saturday, according to a tally by a UN aid agency.
"It is likely to be conservative and it is certainly rising," UNRWA spokesman Christopher Gunness said on Monday. He said the estimate was based on visits by UNRWA officials to hospitals and medical centres across the Gaza Strip.
Hamas defied the strongest assault against Palestinian militants in decades by launching a rocket attack on Israel that killed one person, the second such fatality since Saturday.
Most Gazans in the densely populated enclave stayed at home, in rooms away from windows that could shatter in blasts from air strikes on Hamas facilities. Residents of southern Israel ran for shelter at the sound of alarms heralding incoming rockets.
"At no time could we leave the kids unattended. They trembled every time there was a bombing, day and night, and all of us had almost no sleep," said Umm Hassan, a mother of seven.
An IAF raid flattened a building in the heart of a residential neighborhood in Gaza, sending a cloud of dust into the air, shaking nearby dwellings and wounding five people. It was not immediately clear why the structure, which was apparently empty, was targeted.
Israel declared areas around Gaza a "closed military zone", citing the risk from Palestinian rocket fire, and ordering journalists observing a buildup of armored forces to leave.
"You've got to go," an army spokesman told a Reuters correspondent after she appealed a military police directive to clear out.
Excluding the press could help Israel keep under wraps its preparations for a possible ground assault against Hamas, the Islamist militant group that controls Gaza, following three days of air strikes that have caused chaos, turned some buildings to rubble and left hospitals struggling to cope.