Gaza City - UN Secretary-General Ban Ki-moon said Tuesday he was "deeply grieved" at the scenes he witnessed in Gaza following a three-week Israeli offensive, adding they were "heartbreaking."

He added he was "appalled" also at the damage done to the world body's Gaza City headquarters.

"I'm just appalled. I'm not able to describe how I am feeling at this sight," he said of the compound, which was was struck by several Israeli shells late last week.

"This is heartbreaking," he told a news conference at the headquarters. "I am deeply grieved at what I have seen today."

Ban said he planned to dispatch a humanitarian assessment team to Gaza on Thursday.

"I have condemned on the outbreak of the conflict the excessive use of force by Israeli forces in Gaza," Ban said, adding however that he also viewed Palestinian rocket attacks at southern Israel as "completely unacceptable."

The top UN diplomat called for a "full investigation" into civilians deaths in the war.

"The UN will do all we can," he pledged.

He said Palestinian unity was needed to allow a recovery process and the opening of Gaza's border crossings. (dpa)