Israel says it has allowed five UN lorries carrying humanitarian aid, including baby food, into the Gaza Strip after 11 weeks of blockade.
The UN's humanitarian chief welcomed the move but stressed it was only "a drop in the ocean of what is urgently needed" by the 2.1 million Palestinians in the war-torn territory, where global experts are warning of a looming famine.
Prime Minister Benjamin Netanyahu said his decision to temporarily let in a "minimal" amount of food followed pressure from allies in the US Senate.
"We must not reach a situation of famine, both from a practical and a diplomatic standpoint," he stressed in a video in response to criticism of the move in Israel.
Netanyahu said food deliveries would continue only until the Israeli military and private companies had set up hubs to distribute aid under a US-backed plan rejected by the UN.
He also declared that Israeli forces would "take control of all areas" of Gaza as part of the expanded ground offensive against Hamas that the Israeli military began on Sunday.
Meanwhile, Israeli air strikes killed at least 40 people across the territory on Monday, according to first responders and hospitals.
One strike reportedly killed five people at a school being used as a shelter for displaced families in Nuseirat refugee camp, in central Gaza.
The Israeli military said it struck "Hamas terrorists" who were operating inside a command-and-control centre in the area.
It also ordered the evacuation of the southern city of Khan Younis and its eastern suburbs, warning residents that it was about to launch an "unprecedented attack" there.