US President Donald Trump said that if all the hostages held in Gaza aren't returned by midday Saturday, the ceasefire agreement between Israel and Hamas should be cancelled.
Trump said it was ultimately up to Israel. But he warned that "all hell is going to break out" if the remaining hostages aren't released, adding that he feared many were dead.
Hamas was due to release further hostages on Saturday in exchange for Palestinian prisoners.
But the Palestinian militant group announced on Monday that it would pause the hostage release until further notice. It accused Israel of violating the Gaza ceasefire agreement.
Israeli army raises readiness level around Gaza
The Israeli military said it would increase readiness and "significantly reinforce" areas around the Gaza Strip after Hamas said it was indefinitely delaying the release of Israeli hostages, accusing Israel of violating the ceasefire.
"The reinforcement of forces will strengthen the defense in the area and enhance the readiness for various scenarios in the region," the Israel Defense Forces (IDF) wrote on X.
The military also said it would postpone leave for combat soldiers and operational units within the southern command.