The Israeli military said air raids hit 50 targets in Gaza overnight.
Amid the continuing assault, six more Palestinians, including one baby, were killed in an Israeli air raid in the northern part of the Gaza Strip early on Friday.
Three more Palestinians were killed in shelling in central Gaza, raising the Palestinian death toll in Gaza to 778, including more than 200 children, since the Israeli offensive began on December 27.
More than 3,250 people have also been wounded.
Thirteen Israelis, including three civilians, have been killed in the same period and Hamas said it fired 25 rockets and 12 mortars at Israel on Thursday.
The AFP news agency on Friday said the United Nations had cited witness accounts saying Israeli forces had moved about 110 Palestinians into a house which they then shelled 24 hours later, killing about 30 people.
AFP quoted an unidentified UN official as saying "according to several testimonies, on January 4, Israeli foot soldiers evacuated approximately 110 Palestinians into a single-residence house in Zeitun, warning them to stay indoors.
"Twenty-four hours later, Israeli forces shelled the home repeatedly, killing approximately 30."
The UN Office for the Coordination of Humanitarian Affairs (OCHA) called it "one of the gravest incidents since the beginning of operations" by Israeli forces in Gaza.
The dire humanitarian situation was not improving, our correspondent added, saying that aid agencies had made it clear that they could not act unless Israel provided them better security.
UN aid suspended
On Thursday, the United Nations suspended its aid operations in the Gaza Strip in the wake of a series of Israeli attacks on its personnel and buildings.
"Unrwa decided to suspend all its operations in the Gaza Strip because of the increasing hostile actions against its premises and personnel," Adnan Abu Hasna, a Gaza-based spokesman for the United Nations Relief and Works Agency, said on Thursday.
|The Red Cross says Israel has failed to meet its humanitarian law obligations [Reuters]
The move came after Israeli tanks shelled a UN convoy earlier in the day, killing a Palestinian UN worker and injuring two others, as lorries were travelling to the Erez crossing to pick up humanitarian supplies meant to have been allowed in during a three-hour suspension of fire.
At least three UN-run schools have also been hit by Israeli fire, killing scores of civilians, during the 13 days of Israel's assault on the Gaza Strip.
John Ging, the head of Unrwa in Gaza, said the casualties in Thursday's convoy attack were Palestinian civilian contractors hired to bring supplies from the crossing points.
"They were co-ordinating their movements with the Israelis, as they always do, only to find themselves being fired at from the ground troops," he told Al Jazeera.
"We've lost confidence. We have been reassured continuously over the last number of days that these incidents will not reoccur, and I have taken that in good faith because of the humanitarian imperative.
"We want to believe we are safe here ... but the bottom line is that I've lost confidence in the Israeli side and that needs to be restored urgently, and it is their duty to restore this confidence," Ging said.
All convoys to Erez and the Kerem Shalom, which has been the main crossing point used for bringing humanitarian supplies into Gaza, were suspended after the incident.
The Israeli military said it was looking into reports of Thursday's incident.
Also on Thursday, Israel said it halted its military operations for three hours to allow humanitarian aid into the strip.
The Israeli military, however, faced accusations from the International Committee for the Red Cross (ICRC) of not helping wounded Palestinians in an incident in Gaza City.
ICRC and Palestinian Red Crescent workers said in a statement that several wounded Palestinians and four weakened children were found alongside 12 dead bodies in houses hit by shelling in Zaytun, less than 100 metres from Israeli positions.
"The ICRC believes that in this instance the Israeli military failed to meet its obligation under international humanitarian law to care for and evacuate the wounded," it said.
The Red Cross team, including four ambulances, had only gained safe passage from Israeli army to access the neighbourhood on January 7 after trying for four days, the ICRC said.