Israeli occupation warplanes bombed neighborhood after neighborhood in the Gaza Strip on Tuesday, reducing buildings to rubble and sending people scrambling for safety in the small, enclosed area now suffering severe retaliation for a deadly attack by Hamas militants over the weekend.

Humanitarian groups pleaded for the creation of corridors to get aid into Gaza and warned that hospitals overwhelmed with wounded people were running out of supplies. Israel has stopped entry of food, fuel and medicines into Gaza, and the sole remaining access from Egypt shut down Tuesday after airstrikes hit near the border crossing.

The war, which has claimed at least 1,900 lives on both sides, is expected to escalate. The weekend attack that Hamas said was retribution for worsening conditions for Palestinians under Israeli occupation has inflamed Israel’s determination to crush the group’s hold in Gaza. New exchanges of fire over Israel’s northern borders with militants in Lebanon and Syria on Tuesday pointed to the risk of an expanded regional conflict.

Hamas militants stormed into Israel on Saturday morning, slaying hundreds of residents in homes and streets near the Gaza border and bringing gunbattles to Israeli towns for the first time in decades. Hamas and other militant groups in Gaza hold about 150 soldiers and civilians hostage, according to Israel.

Israel stepped up its offensive on Tuesday, expanding the mobilization of reservists to 360,000. Israel’s military said it had regained effective control over areas Hamas attacked in its south and of the Gaza border.

A looming question is whether Israel will launch a ground assault into Gaza — a 40-kilometer-long (25-mile) strip of land wedged among Israel, Egypt and the Mediterranean Sea that is home to 2.3 million people and has been governed by Hamas since 2007.