Israel launched airstrikes across the Gaza Strip early Tuesday, killing more than 400 Palestinians, local health officials said, and shattering a ceasefire in place since January with its deadliest bombardment in a 17-month war with Hamas.

Israel says the offensive is due to Hamas’ refusal to release hostages, vowing to increase military pressure if talks continue to stall.

Israel said it recaptured an area from which it withdrew in the recent cease-fire, in the most significant ground operation since the truce with Hamas collapsed.

Israeli Defence Minister Israel Katz said on Friday the army was intensifying strikes from the air, land and sea in Gaza to pressure Hamas into freeing remaining hostages, and would also evacuate civilians to the south of the enclave.

Hamas fired rockets at Israel from Gaza Thursday, the militant group’s first response to Israel’s renewed offensive in the Strip that shattered the two-month-old ceasefire.