Israeli forces have driven their military offensive deeper inside heavily populated areas of Gaza City, striking at the southern district of Tel al-Hawa, a stronghold of support for the Hamas movement.
Buildings reported to have been hit include a Red Crescent hospital and a building housing media organisations, including Associated Press, from whose office this photograph was taken.
The UN building in southern Gaza City was rocked by several explosions. Officials said munitions were fired after the UN had repeated warnings to the Israel army it was a civilian location.
The UN accused Israel of firing white phosphorus (WP) at its centre - in violation of the laws of war - but Israel denies using illegal weaponry. Observers say some shell bursts were consistent with WP.
Thousands of civilians have fled the area of the bombardment fearing for their lives, although many were reported to be still trapped in their homes or other shelters.
Israel said it was taking care to avoid harming civilians and blamed Hamas militants for hiding among the ordinary Palestinian population.
Large numbers of civilians in Gaza are sheltering in public buildings such as this UN-run school in Jabalia refugee camp.
Aid agencies have been warning of a severe humanitarian crisis where even before Israel's offensive began on 27 December there were shortages of food, fuel and essential supplies.