At least 40 Palestinians were killed by Israeli strikes across Gaza on Sunday, including two dozen when a residential building in the northern town of Jabalia was hit, Palestinian health officials and a human rights group said.

The Palestinian Center for Human Rights (PCHR) in Gaza said at least 24 people were killed when an Israeli strike destroyed the three-story building in Jabalia at dawn. Thirty other people from nearby houses were wounded, PCHR said in a statement.

The Israeli military said it struck a site in Jabalia where "terrorists were operating."

"These terrorists posed a threat to IDF (Israeli Defence Forces) troops operating in the area. The details are under review," the Israeli military said.

In Gaza City, an Israeli air strike on a house in the Sabra neighborhood on Sunday killed Wael Al-Khour, an official at the welfare ministry, as well as his wife, Khour, one son, two daughters and three grandchildren, medical officials and relatives said.

The Israeli military said it was looking into the report.

The Palestinian Red Crescent Society said its teams, in collaboration with the International Committee of the Red Cross, evacuated 20 patients from Al-Awda Hospital in Jabalia on Sunday to another facility in Gaza City.

It said one of the patients died because the ambulances were held up for hours at an Israeli checkpoint separating northern Gaza areas from Gaza City.

The three hospitals in and around Jabalia have been besieged by Israeli forces for several weeks, and hospital officials have refused army orders to evacuate the facilities or leave their patients unattended despite the depletion of food, medical and fuel supplies.

The Israeli military accuses the Palestinian militant group Hamas of exploiting the civilian population and property in Gaza for military purposes, a charge the militant group denies.

Hamas' armed wing said it killed 15 Israeli soldiers in an attack in the city of Beit Lahiya, north of Jabalia, on Sunday.

There has been no comment from Israel, Reuters reported, adding it could not independently verify the account.

Children aged five to nine account for most verified Gaza deaths

The UN Human Rights Office said on November 8 that nearly 70 percent of the fatalities it has verified in the Gaza war were women and children and condemned what it called a systematic violation of the fundamental principles of international humanitarian law.

The UN tally since the start of the war, in which Israel's military is fighting Hamas militants, includes only fatalities it has managed to verify with three sources, and counting continues.

This finding indicates "a systematic violation of the fundamental principles of international humanitarian law, including distinction and proportionality," the UN rights office said in a statement accompanying the 32-page report.

The youngest victim, whose death was verified by UN monitors, was a one-day-old boy, and the oldest was a 97-year-old woman, the report said.

Overall, those aged 18 or under represent 44 percent of the victims, with children aged five to nine representing the single biggest age category, followed by those aged 10-14, and then those aged up to and including four.

(With input from Reuters)