Israeli attacks have killed 97 people in the Gaza Strip, raising the overall Palestinian death toll to 435 since the start of a major military campaign on July 8, Palestinian health officials say, as the military wing of Hamas claims it has abducted an Israeli soldier.
The vast majority of Sunday's dead were in Shujayea, a district between Gaza City and the Israeli border, with at least 60 people killed there in an intense bombardment which began overnight.
Besides Shujayea, where bodies littered the streets, the worst hit neighbourhoods were al-Shaaf and al-Tuffa.
A Shujayea resident who reached a hospital told Al Jazeera: "It is a massacre taking place in Shujayea. It is a massacre - in the full sense of the word - committed by Israel against innocent civilians. There are no armed men among us. The streets of Shujayea are packed with dead bodies."
At least 250 others were wounded in Sunday's barrage, raising the overall Palestinian injury toll during the 13 days of violence to well above 3,000, Ashraf al-Qudra, a Gaza emergency services spokesman, said.
Palestinian President Mahmoud Abbas described the Shujayea deaths as "a massacre" and declared three days of mourning.
Of the 435 people killed in Gaza since the Israeli military offensive began, more than a third were women and children, Qudra said, indicating that 112 of the victims were minors, 41 were women and 25 were elderly.
For its part, the Israeli army announced on Sunday the deaths of 13 soldiers in fighting in Gaza, just hours before the al-Qassam Brigades, the military of Hamas, claimed it had abducted an Israeli soldier, Shaul Aaron.
Israel has not commented on the abduction claim.
"Over the course of the day, 13 soldiers from the IDF's Golani Brigade were killed in combat in the Gaza Strip," an army statement said.
Sunday's deaths raised to 18 the total number of Israel soldiers killed since they began a ground operation in Gaza late on Thursday, in what was the highest casualty figure since the 2006 Lebanon war.
Dozens more have been wounded.
Sunday's violence raised the overall Israeli death toll to 20, which includes two civilians killed by rocket fire.
Early on Sunday afternoon, Israel agreed to observe a two-hour humanitarian ceasefire in Shujayea to allow the evacuation of wounded, but it was broken less than an hour after it was announced.
Israel's military said it resumed combat operations after its forces were shot at shortly after the two-hour truce facilitated by the Red Cross took effect at 1.30pm local time.
Hamas, the Palestinian group, said earlier it would abide by the temporary truce.
Al Jazeera's Stefanie Dekker witnessed desperate civilians making their way into Gaza City on Sunday morning.
"While driving into the bureau, we were met by hundreds of people on foot carrying their children, carrying plastic bags filled with whatever belongings they could take with them," she said.
"They couldn't leave during the night."
Dozens of bodies were brought to hospitals from Shujayea on Sunday morning, and more were expected to arrive after ambulances could access the neighbourhoods.
Those killed included senior Hamas leader Khalil al-Hayya's son Osama, his wife Hala and their two children.
Overnight Israeli shelling
Israel says it launched its offensive in response to rockets fired from Gaza, and that it is targeting military installations of Hamas and other armed groups.
However, the vast majority of those killed and injured are Palestinian civilians, many of them children.
Speaking to Al Jazeera, Waleed, a resident of Gaza's al-Shaaf neighbourhood, said he was terrified and stuck with his family of 18 members in a single room and had nowhere to go while Israeli shelling continued through the night.
"We can hear shells and rockets fall on our streets and homes. They are falling everywhere," he said.
"We have no electricity, everything has been cut off. The Red Cross can't reach the area - it's too dangerous. People are stuck at home. All we hear is shelling."
Mads Gilbert, a Norwegian doctor working at al-Shifa hospital, told Al Jazeera that most of the casualties brought there were civilians who suffered shrapnel injuries and amputations.
"It's very disturbing to see the large number of civilians, particularly the children. What is remarkable with the Palestinians in Gaza is the resilience. They don't give up, they stand tall. I'm amazed to see the calm and coherence in the community and in the hospital among the [hospital] staff," Gilbert said.
"What [Palestinians] are [saying] is that how can the world accept the Israelis targeting civilians in an area which is completely shut off? There are no shelters, no early-warning systems, no sirens. The population is basically completely naked to the enormously strong Israeli military machine."