Forty-two people have died in the latest Israeli air strikes on Gaza, as the conflict with Palestinian militants entered its seventh day.
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.
Since it began on Monday at least 188 people have been killed in Gaza, including 55 children and 33 women, with 1,230 injured, according to the Hamas-controlled health ministry. Israel says dozens of militants are among the dead.
Ten people, including two children, have been killed by militant attacks on Israel, Israeli officials say.
The Israeli air strikes - the deadliest attack in the conflict so far - hit a busy street just after midnight on Sunday.
Palestinian rescue workers have been working through the rubble of at least three destroyed buildings, pulling out bodies and searching for survivors.
"I have never covered air strikes with such intensity, explosions are everywhere in Gaza, there are difficulties in communicating with officials to find out where the strikes are," said the BBC's Rushdi Abualouf in Gaza.
"The building in which I live in [the] western part of the city shook like an earthquake," he wrote on Twitter. "A hysterical state of chaos, children and women in the building that houses more than 200 people screaming."
Israel's military said it struck the homes of both Hamas leader Yahya Sinwar and his brother Muhammad Sinwar, whom it described as head of logistics and manpower for the movement.
Both residences had, it said, "served as military infrastructure" for Hamas.
Local sources confirmed to media that the Hamas leader's home in the Gaza town of Khan Younis had been bombed. There were no immediate reports about the fate of the two brothers.
It was unlikely they were at home at the time of the strikes, according to the Associated Press news agency.