A senior political source said that Israel will "respond with strength" should Hamas make good on its promise to renew rocket fire as soon as soon as the ceasefire end 8 am Friday morning.
"Prime Minister Benjamin Netanyahu and Defense Minister Moshe Ya'alon have given the IDF directives for any scenario," the senior source said.
- Hamas military wing: No to extending ceasefire
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- Lieberman: Hamas threat to resume fire is coercion
Foreign Minister Avigdor Liberman accused Hamas of coercion on Thursday, after the organization's official denied reports of an extension to the ceasefire.
The comments came as an Egyptian source told AP that the Palestinian delegation to the ceasefire talks in Cairo had hardened its position after Hamas and Islamic Jihad leaders arrived.
Speaking to US Secretary of State John Kerry overnight, Foreign Minister Avigdor Lieberman said the Palestinians' announcement that they would resume fire as soon the current lull ends was "coercive" and that "Israel will take this into account and is prepared for any eventuality."
Lieberman thanked Kerry "for the United States' unequivocal support for Israel during the discussion held yesterday at the United Nations General Assembly. Thanks to the concerted effort, the adoption of a binding anti-Israeli resolution was prevented."
Mediators worked against the clock on Thursday to extend a truce between Israel and Palestinian militants in Gaza, as the three-day ceasefire went into its final 24 hours.
Israel said it was ready to agree to an extension as Egyptian mediators pursued talks with Israelis and Palestinians on ending a war that has devastated the Hamas-ruled enclave. Palestinians want an Israeli-Egyptian blockade of Gaza to be lifted and prisoners held by Israel to be freed.
“Indirect talks are ongoing and we still have today to secure this,” an Egyptian official said when asked whether the truce was likely to go beyond Friday.
“Egypt’s aims are to stabilize and extend the truce with the agreement of both sides and to begin negotiations towards a permanent agreement to cease fire and ease border restrictions.”
The Palestinian delegation was expected to meet Egyptian intelligence officials late on Thursday evening.
After a month of bitter fighting, the two sides are not meeting face to face.
Gaza officials say the war has killed 1,874 Palestinians, most of them civilians. Israel says 64 of its soldiers and three civilians have been killed since fighting began on July 8, after a surge in Palestinian rocket salvoes into Israel.
An Israeli official said late on Wednesday that Israel "has expressed its readiness to extend the truce under its current terms" beyond Friday morning's expiry of the three-day deal, which took effect on Tuesday and has so far held.
A senior Israeli minister, Yaakov Peri, said on Army Radio that an extension would be "right for both sides" and added: "Let's hope that reason prevails."
Reuters contributed to this report