The fatalities included 12 people who drowned in the sea in the northern Gaza Strip and six in a stampede while gathering to obtain aid, the office said in a statement.
“The aid airdrops pose a real threat to the lives of hungry Palestinians,” the statement warned.
It said some aid fell into the sea, inside Israel or in war zones.
“This all put the lives of people in real danger,” the office added.
Israel has imposed a crippling blockade on the Gaza Strip since last October, leaving most of its population, particularly residents of the north, on the verge of starvation.
As Tel Aviv maintained its siege on the enclave, several countries began to airdrop humanitarian aid into several areas in Gaza to avert famine in the territory.
Israel has waged a deadly military offensive on the Palestinian territory since a cross-border attack by the Palestinian group Hamas in which some 1,200 Israelis were killed.
More than 32,333 Palestinians have since been killed and over 74,694 injured amid mass destruction and shortages of necessities.
On Monday, the UN Security Council passed a resolution demanding an immediate cease-fire in Gaza during the Islamic holy month of Ramadan.
While Hamas welcomed the resolution, Israel rejected the cease-fire call and vowed to continue its war on the Palestinian enclave.
The Israeli war, now in its 172nd day, has pushed 85% of Gaza’s population into internal displacement amid acute shortages of food, clean water and medicine, while 60% of the enclave's infrastructure has been damaged or destroyed, according to the UN.
Israel is accused of genocide at the International Court of Justice. An interim ruling in January ordered Tel Aviv to stop genocidal acts and take measures to guarantee that humanitarian assistance is provided to civilians in Gaza.