Israeli Prime Minister Benjamin Netanyahu says fighting against the Islamic group Hamas will continue for "many more months."
He spoke at the start of a Cabinet meeting on Sunday, the 100th day since the conflict began following Hamas' assaults on Israeli communities on October 7.
People in Israel marked the day by ringing bells to pray for the safety and early return of all remaining hostages still held in the Gaza Strip.
Netanyahu said his government is "not giving up" on any hostages and is "doing everything" to bring every one of them home.
Palestinian media say the Israeli military unleashed airstrikes and shelling across Gaza on Sunday, causing many casualties.
Health officials in Gaza say Israeli attacks have left 125 people dead over the past 24 hours, raising the death toll in the enclave over the last 100 days to 23,968.
The Lebanon-based Shia militant group Hezbollah, which pledges solidarity with Hamas, is taking an increasingly confrontational stance toward Israel.
A missile attack by Hezbollah claimed the lives of two residents in northern Israel on Sunday, while the Israeli military says it killed four militants who had crossed into Israel.
Hezbollah leader Hassan Nasrallah gave a speech on Sunday, saying "the Lebanon front has been for supporting and assisting Gaza." He also said Hezbollah has been "ready for war for the past 99 days" and that the group does "not fear it."