The United States renewed concern Friday about an Israeli assault on Rafah but said it saw no major operation yet against the packed Gaza city and still held out the possibility of a ceasefire deal.

"We're obviously watching it with concern," National Security Council spokesman John Kirby said of the latest Israeli military strikes around Rafah.

"But I wouldn't go so far as to say what we've seen here in the last 24 hours connotes or indicates a broad, large (or) major ground operation," he said.

"It appears to be localized near the crossing and largely with the forces that they had put in there at the beginning."

President Joe Biden on Wednesday warned Israel of a halt in weapons from the United States, its primary ally, if it went into Rafah, where some 1.4 million displaced Palestinians are sheltering.

Israel has also seized the Rafah crossing into Egypt from Hamas militants. The closure of the border has raised new concerns about aid delivery into Gaza, where the United Nations has warned of famine risks.

"Once again, we urge the Israelis to open up that crossing to humanitarian assistance immediately. That aid is desperately needed," Kirby said.

"And we urge them, as we have in the past, to be as careful, precise and discriminate as they can here so that they are not putting innocent lives at greater risk than they already are."

Kirby said the United States was still holding out hope for a ceasefire after CIA Director Bill Burns, the US pointman on the negotiations, left the region following talks in Cairo.

Kirby said it was "deeply regrettable" that there was "nobody sitting across from tables anymore today."

"We are working hard to try to keep both sides engaged in and continuing the discussion, if only virtually, and to continue to work on the actual text itself," he said.

"We still believe that a deal was possible."