The United States does not believe that genocide is occurring in Gaza but Israel must do more to protect Palestinian civilians, President Joe Biden's top national security official said Monday.

As ceasefire talks stall and Israel continued striking the southern city of Rafah, White House National Security Advisor Jake Sullivan insisted that the responsibility for peace lay with militant group Hamas.

"We believe Israel can and must do more to ensure the protection and wellbeing of innocent civilians. We do not believe what is happening in Gaza is a genocide," Sullivan told a briefing.

The US was "using the internationally accepted term for genocide, which includes a focus on intent" to reach this assessment, Sullivan added.

Biden wanted to see Hamas defeated but realized that Palestinian civilians were in "hell", Sullivan said.

Sullivan said he was coming to the White House podium to "take a step back" and set out the Biden administration's position on the conflict, amid criticism from both ends of the US political spectrum.

Biden has come under fire from Republicans for halting some weapons shipments to press his demands that Israel hold off a Rafah offensive, while there have been protests at US universities against his support for Israel.

The US president believed any Rafah operation "has got to be connected to a strategic endgame that also answered the question, 'what comes next?'" Sullivan added.

This would avoid Israel "getting mired in a counterinsurgency campaign that never ends, and ultimately saps Israel's strength and vitality."