After Israel began ground operations in Rafah, a move staunchly opposed by most Western allies, the flow of critical aid into Gaza has ground to a near halt.

“The closure of both the Rafah and Kerem Shalom crossings is especially damaging to an already dire humanitarian situation,” said United Nations Secretary-General António Guterres. “They must be re-opened immediately. [...] Rafah is the epicentre of humanitarian operations in Gaza.”

Israel's military said on Monday it had begun encouraging residents of Rafah to evacuate the southern Gazan city as part of a “limited scope” operation.

On Tuesday, Israel said its forces had seized the critical Rafah crossing, the only route into Gaza for international aid not previously controlled by Israeli forces.

Israel says its planned assault on Rafah is to defeat thousands of Hamas fighters it says are there, but on Wednesday U.S. President Joe Biden warned that if Israel launched a full-scale invasion of the city in the southern Gaza Strip it would do so without U.S. supplied weapons, his strongest comments to date criticising Israel’s conduct in the conflict.

The U.N. warned that fuel was especially scarce across Gaza and could further drive the developing humanitarian disaster in the enclave.

“If no fuel comes in for a prolonged period of time it would be a very effective way of putting the humanitarian operation in its grave,” said U.N. spokesperson Jens Laerke.

While some non-fuel supplies have entered Gaza via the northern Erez crossing in recent days, the U.N. agencies said this was insufficient and difficult to deliver to Rafah, where a million Gazans are sheltering since Israeli military operations drove them out of northern Gaza, since it meant crossing active combat zones.

“Erez will simply not be enough,” said James Elder, a spokesperson for the United Nations children's agency. “If Rafah gate closes for an extended period, it's hard to see how famine in Gaza can be averted.”