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.

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, 73 Palestinians, including 37 civilians, have been killed in the five-day onslaught. Three Israeli civilians have also died from Palestinian rocket fire.

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.

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.

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.

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.

Israel sought to place the blame on militants, saying they were intentionally operating in places inhabited by civilians.

“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.

Obama blamed Palestinian militants for starting the round of fighting by raining rockets onto Israel and said the U.S. supported Israel’s right to protect itself. “Israel has every right to expect that it does not have missiles fired into its territory,” Obama said.

Printed on Monday, November 19, 2012 as: Gaza civilians killed in deadliest day