Israel has urged civilians to evacuate “combat zones” in Gaza, following a second night of bombardment in the enclave.

The IDF warned Palestinians to make their way to “known shelters” on Wednesday, raising expectations of further strikes or a possible ground offensive.

The Israeli Air Force said it hit 20 targets, including a Hamas military site in northern Gaza where rockets were being prepared.

The Navy also said it attacked boats belonging to Hamas and Palestinian Islamic Jihad off the coast.

Hamas said 13 people were killed by the action, adding to the total of more than 400 after Israel broke the ceasefire with its surprise attack on Tuesday night.

The group also said a foreign national had been killed in an airstrike on a UN facility in central Gaza.

The bombardment restarted, following nearly two months of peace, after negotiations on the release of further hostages failed to find agreement.

Israel is hoping that by attacking Hamas and its civilian infrastructure it can force them to take seriously a US proposal to release more hostages, without having to withdraw its forces completely from the Strip.

On Wednesday, a spokesman for Hamas said it “has not closed the door on negotiation”, adding: “we insist there is no need for new agreements”.