Arbour was speaking not far from the Nasser mosque, one of the oldest mosques in Gaza whose lone minaret is all that remains after the offensive, before heading into talks with Mahmoud Abbas, the Palestinian president, at his Gaza City seafront office.
She emphasised that she would stress to both Israeli and Palestinian authorities the need to protect civilians.
More than 60 Palestinians were killed during a six-day Israeli operation in Beit Hanoun. Nineteen others, mostly women and children, died in an Israeli shelling on November 8.
Arbour's visit comes less than a week after the UN Human Rights Council voted last Wednesday to send an urgent fact-finding mission to Beit Hanoun to examine the impact of Israel's attack on the Palestinian homes.
Thirty-two countries, mainly from Asia, Africa and the Middle East, voted for the resolution introduced by Arab and Islamic nations at the 47-member Council, which was subsequently denounced by Washington as "imbalanced".