JERUSALEM -- The United Nations on Friday cited witnesses saying Israeli forces evacuated about 110 Palestinians into a house which they then repeatedly shelled 24 hours later, killing about 30 people.

It said that "according to several testimonies, on 4 January Israeli foot soldiers evacuated approximately 110 Palestinians into a single-residence house in Zeitun [half of whom were children] 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 on December 27.

"Those who survived were able walked two kilometers to Salah Ed Din road before being transported to hospital in civilian vehicles. Three children, the youngest of whom was five months old, died upon arrival at the hospital," OCHA said in a report on the situation in the battered Gaza Strip.

Asked for comment, an Israeli military spokesman said the allegation was being investigated, as were other claims that civilians were fired upon and that troops failed to help wounded civilians.