"Damage to hospitals, schools and UNRWA shelters where people displaced sought refuge will take months to rebuild," she said, referring to the United Nations agency for Palestinian refugees.
Amos was speaking to reporters at the start of a two-day visit for talks with Iranian officials on the humanitarian crises wreaked by conflicts in the Gaza Strip, Syria and Iraq.
"The UN response continues including deliveries of food, water and households goods. Medicines and fuel are being delivered to hospitals," she said.
The conflict, in which an Egyptian-mediated ceasefire has taken effect, has killed almost 2,000 Palestinians, mostly civilians, and 67 on the Israeli side, almost all soldiers.
More From This Section
Amos noted the United Nations had made "strong statements" about "the violation of international humanitarian laws and human rights laws by all parties in Gaza".
Turning to Syria, she said that 11 million people were in need of humanitarian aid, including 241,000 living in areas under siege.
Amos welcomed the role played by Iran, a key ally of the Syrian government, and other countries with influence on the warring parties to gain access to conflict zones.
"This remains a work in progress because we still have substantial numbers of people that we are unable to reach," she said.