Israeli Prime Minister Benjamin Netanyahu said "intense fighting" would resume in Gaza if Hamas did not return hostages by noon Saturday, without specifying whether he was referring to all captives, or only the three that had originally been planned for release.
The ceasefire was called into question when Hamas claimed Monday that Israel had violated key provisions, prompting it to cancel the release of three more hostages on Saturday.
"If Hamas does not return our hostages by Saturday noon, the ceasefire will end, and the IDF (Israeli Defense Force) will resume intense fighting until Hamas is decisively defeated," Netanyahu said in a video statement issued after a meeting with his security cabinet.
After Netanyahu's statement, the Israeli military said it would deploy additional forces south.
"It was decided to increase reinforcements with additional troops, including reservists", the IDF said in a statement on Tuesday, adding the move was "carried out in preparation for various scenarios."