Gaza health officials said 16 women and 10 children were among the dead.
Israel's military said it had been targeting leaders and infrastructure linked to Hamas, the militant group that runs Gaza.
Hamas launched a new barrage of rockets towards southern Israel on Sunday afternoon.
Meanwhile, a UN Security Council meeting has begun, with international mediators hoping to broker a ceasefire.
UN Secretary-General Antonio Guterres opened the meeting by describing the violence as "utterly appalling" and said the fighting must stop immediately.
