Dozens of people have been killed and wounded in an Israeli attack on a house in Jabalia in northern Gaza, Palestinian medics and rescuers say.
The official Palestinian news agency Wafa and Gaza's Hamas civil defense agency said at least 33 people had been killed. The civil defense said that among the dead were 13 children.
The Israel Defense Forces (IDF) said it struck a site in Jabalia where "terrorists were operating", steps had been taken to mitigate civilian casualties and details were under review.
Aid groups say Jabalia and other parts of northern Gaza have been under siege since early October, when Israel launched a new ground offensive against Hamas.
Israel is facing a US deadline that expires within days to improve the humanitarian situation in Gaza or face possible restrictions on military cooperation.
Dr Fadel Naim, director of Al-Ahly Hospital in Gaza City, told the AP news agency that the hospital where he worked had received 17 bodies from Jabalia so far, including those of nine women, and the death toll was likely to increase.
Eyewitnesses described the Israeli strike on the building said to have belonged to the Alloush family as an "earthquake".
"We were just sitting quietly. These are innocent citizens who do not belong to any military organization or faction," eyewitness and relative of the victims Hamza Alloush told Reuters.