GAZA CITY, Gaza Strip — Israeli aircraft struck crowded areas in the Gaza Strip and killed a senior militant with a missile strike on a media center Monday, driving up the Palestinian death toll to 100, as Israel broadened its targets in the six-day-old offensive meant to quell Hamas rocket fire on Israel.

Escalating its bombing campaign during the weekend, Israel began attacking homes of activists in Hamas, the Islamic militant group that rules Gaza. These attacks have led to a sharp spike in civilian casualties, killing 24 civilians in just under two days and doubling the number of civilians killed in the conflict, a Gaza health official said.

The rising toll came as Egyptian-led efforts to mediate a cease-fire between Israel and Hamas got into gear.

While Israel and Hamas were far apart in their demands, both sides said they were open to a diplomatic solution — and prepared for further escalation if that failed.

The leader of Hamas took a tough stance, rejecting Israel’s demands that the militant group stop its rocket fire. Instead, Khaled Mashaal said, Israel must meet Hamas’ demands for a lifting of the blockade of Gaza.

“We don’t accept Israeli conditions because it is the aggressor,” he told reporters in Egypt. “We want a cease-fire along with meeting our demands.”

An Israeli official said Israel hoped to find a diplomatic solution to the crisis as well and signaled Egypt was likely to play a key role in enforcing any truce.

“We prefer the diplomatic solution if it’s possible. If we see it’s not going to bear fruit, we can escalate,” he said, speaking on condition of anonymity because of the sensitive diplomatic efforts under way.

The official said Israel doesn’t want a “quick fix” that will result in renewed fighting months down the road. Instead, Israel wants “international guarantees” that Hamas will not rearm or use Egypt’s neighboring Sinai peninsula for militant activity.

Overall, the offensive that began Wednesday killed 100 Palestinians, including 53 civilians, and wounded some 840 people, including 225 children, Gaza heath official Ashraf al-Kidra said.

On the Israeli side, three civilians have died from Palestinian rocket fire and dozens have been wounded. A rocket-defense system has intercepted hundreds of rockets bound for populated areas.

Hamas fighters have fired more than 1,000 rockets into Israel in the current round of fighting, including 95 on Monday, among them one that hit an empty school in the coastal city of Ashkelon. Israeli police spokesman Micky Rosenfeld said 29 rockets were intercepted by the Iron Dome anti-missile battery. Rockets landed in open areas of Beersheva, Ashdod, Ashkelon, and caused damage in a number of areas.

Schools in southern Israel have been closed since the start of the offensive on Wednesday, and large police units deployed in the area to respond to any potential damage and injuries from rockets.

A poll published in the Haaretz daily on Monday showed widespread support in Israel for the offensive. It said that 84 percent of the public supports the operation, with 12 percent opposed. At the same time, it said just 30 percent of the public supports a ground invasion of Gaza. The poll, conducted by the Dialog agency, surveyed 520 people and had a margin of error of 4.4 percentage points.