GAZA CITY, Gaza Strip -- An Israeli missile ripped through a two-story home in a residential area of Gaza City on Sunday, killing at least 11 civilians, including four young children and an 81-year-old woman, in the single deadliest attack of Israel's offensive against Islamic militants.
A similar scene unfolded elsewhere in the city early Monday, when an airstrike leveled two houses belonging to a single family, killing two children and two adults and injuring 42 people, including children, said Gaza heath official Ashraf al-Kidra. Rescue workers were frantically searching for 12 to 15 members of the Azzam family under the rubble.
While the airstrikes relentlessly targeted militant rocket operations, Israeli gunboats unleashed a steady tattoo of heavy machine gun fire and shells at militant facilities on Gaza's coastal road.
The bloodshed was likely to raise pressure on Israel to end the fighting, even as it pledged to intensify the offensive by striking the homes of wanted militants. High numbers of civilian casualties in an offensive four years ago led to fierce criticism and condemnation of Israel.
In all, 81 Palestinians, half of them 37 civilians, have been killed in the five-day onslaught and 720 have been wounded. Three Israeli civilians have died from Palestinian rocket fire and dozens have been wounded..
President Barack Obama said he was in touch with players across the region in hopes of halting the fighting, while also warning of the risks of Israel expanding its air assault into a ground war.
"We're going to have to see what kind of progress we can make in the next 24, 36, 48 hours," Obama said during a visit in Thailand.
U.N. chief Ban Ki-moon urged the two warring parties to achieve an immediate cease-fire. He said he was heading to the region to appeal personally for an end to the violence, but no date was given in the U.N. statement for his arrival.
On the ground, there were no signs of any letup in the fighting as Israel announced it was widening the offensive to target the military commanders of the ruling Hamas group.
The Israeli military carried out dozens of airstrikes throughout the day, and naval forces bombarded targets along Gaza's Mediterranean coast. Many of the attacks focused on homes where militant leaders or weapons were believed to be hidden.
Palestinian militants continued to barrage Israel with rockets, firing more than 100 on Sunday, and setting off air raid sirens across the southern part of the country. Some 40 rockets were intercepted by Israel's U.S.-financed "Iron Dome" rocket-defense system, including two that targeted the metropolis of Tel Aviv. At least 10 Israelis were wounded by shrapnel.
Israel's decision to step up its attacks in Gaza marked a new and risky phase of the operation, given the likelihood of civilian casualties in the densely populated territory of 1.6 million Palestinians. Israel launched the offensive Wednesday in what it said was an effort to end months of intensifying rocket fire from the Hamas-ruled Gaza Strip.
In the day's deadliest violence, the Israeli navy fired at a home where it said a top wanted militant was hiding. The missile struck the home of the Daloo family in Gaza City, reducing the structure to rubble.
Frantic rescuers, bolstered by bulldozers, pulled the limp bodies of children from the ruins of the house, including a toddler and a 5-year-old, as survivors and bystanders screamed in grief. Later, the bodies of the children were laid out in the morgue of Gaza City's Shifa Hospital.
Among the 11 dead were four small children and five women, including an 81-year-old, Gaza health official Ashraf al-Kidra said.
More than a dozen homes of Hamas commanders or families linked to Hamas were struck on Sunday. Though most were empty - their inhabitants having fled to shelter - at least three had families in them. Al-Kidra said 20 of 27 people killed Sunday were civilians, mostly women and children.
Sami Abu Zuhri, a Hamas spokesman, said that "the Israeli people will pay the price" for the killing of civilians.
Israel sought to place the blame on militants, saying they were intentionally operating in places inhabited by civilians. The military has released videos and images of what it says are militants firing rockets from mosques, schools and public buildings.
"Hamas is using the Gaza population as human shields," said Brig. Gen. Yoav Mordechai, the chief Israeli spokesman. "They are exploiting crowded residential urban areas."
He acknowledged, however, that it was not clear whether the militant targeted in Sunday's attack was killed, despite earlier claims of success. "I still don't know what became of him," Mordechai told Channel 10 TV.
The prospect of mounting civilian casualties could quickly change the momentum of Israel's operation. Israel launched the offensive on Wednesday with a lightning airstrike that killed Hamas' military chief. Since then, it has carried out a blistering campaign of more than 1,200 airstrikes, targeting suspected rocket storage and launching sites.