US National Security Advisor Jake Sullivan said Friday it is not appropriate for Israel to occupy Gaza in the long-term, as speculation mounts over the post-war future of the territory.

"We do not believe that it makes sense for Israel, or is right for Israel, to occupy Gaza, reoccupy Gaza over the long term," Sullivan told journalists in Tel Aviv.

"Ultimately the control of Gaza, the administration of Gaza and the security of Gaza has to transition to the Palestinians," he said following meetings with senior Israeli officials.

The United States is a key military backer of Israel in its war against Hamas in the Gaza Strip, which erupted on October 7 after an attack by the militant group which killed around 1,200 people in Israel, according to Israeli officials.

Relentless Israeli strikes and a ground invasion of Gaza have killed at least 18,787 people, the health ministry in the Hamas-run territory said in its latest toll.

The majority of casualties are civilians, Israeli and Palestinian officials say.

The US and Israel concur that the war will last months more, Sullivan said, while there are "intensive discussions" about future stages of the conflict and the aftermath.

The White House advisor is due to travel later Friday to the occupied West Bank to meet the Palestinian Authority leader Mahmud Abbas.

Washington has suggested the internationally-recognised PA could play a role in governing Gaza after the war, though the Ramallah-based administration is deeply unpopular among Palestinians.

"We do believe that the Palestinian Authority needs to be revamped and revitalised, needs to be updated in terms of its method of governance, its representation of the Palestinian people," Sullivan said.