The investigation's mandate is to focus only on Palestinian victims of the 22-day war.
More than 1,100 Palestinians were killed when Israel launched a two-week ground offensive on Gaza in December and January after a week of aerial bombardment.
The Palestinian Centre for Human Rights put the final death toll at 1,417, including 926 civilians, and published a list of their names.
The Israeli military, however, says only 295 civilians were among 1,116 Palestinians killed between December 27 and January 18, without providing a list of the dead.
It insists it did everything it could to prevent casualties among Gaza civilians during the war, including dropping leaflets and sending phone messages to civilians to evacuate certain areas.
The military also claims Hamas fighters used civilians as human shields, booby-trapped homes and shot at troops from densely populated areas.
Israeli officials on Friday did not say whether or not they would co-operate with the UN investigation.
It has rejected previous human rights council investigations, including one led by Desmond Tutu, the Nobel Peace Prize laureate, calling them "biased".
The Israeli military earlier in the week closed its own investigation into claims that Israeli troops shot unarmed Palestinian women and children during the Gaza war.
Military investigators said on Monday that they "found crucial components of [the allegations] were based on hearsay and were not supported by specific personal knowledge".